Vine's Expository Dictionary of OT Words 
Pârad ( פָּרַד , Strong'S #6504), “to divide, separate.” This word and its derivatives are common to both ancient and modern Hebrew. It is found in the text of the Hebrew Old Testament only about 25 times. Pârad occurs for the first time in the text in Gen. 2:10: “And a river went out of Eden … and from thence it was parted, and became into four heads.” The meaning here must be “dividing into four branches.”
This word often expresses separation of people from each other, sometimes with hostility: “Separate thyself … from me …” (Gen. 13:9). A reciprocal separation seems to be implied in the birth of Jacob and Esau: “Two nations are in thy womb, and two manner of people shall be separated from thy bowels …” (Gen. 25:23). Sometimes economic status brings about separation: “… The poor is separated from his neighbor” (Prov. 19:4). Generally speaking, pârad has more negative than positive connotations.
Nâzar ( נָזַר , Strong'S #5144), “to separate, be separated.” This verb occurs about 10 times in the Old Testament. The root nâzar is a common Semitic verb. In Akkadian, nâzaru meant “to curse,” but in West Semitic it connoted “to dedicate.” Students of Semitic languages often relate Hebrew nâzar to nadhar (“to vow”).
“To separate” and “to consecrate” are not distinguished from one another in the early Old Testament books. For example, the earliest use of nâzar in the Pentateuch is in Lev. 15:31: “Thus shall ye separate the children of Israel from their uncleanness; that they die not in their uncleanness, when they defile my tabernacle that is among them.” Here Moses uses the word in a cultic sense, meaning a kind of “consecration.” A comparison of various twentieth-century translations will show that nâzar in Lev. 22:2 is sometimes rendered “to separate,” and sometimes “to dedicate.” The NIV translates this verse: “Tell Aaron and his sons to treat with respect the sacred offerings the Israelites consecrated to me, so that they will not profane my holy name. I am the Lord.”
In the days of the prophet Zechariah, Jews asked the Lord whether certain fasts which they had voluntarily adopted were to be continued and observed. “When they had sent unto the home of God Sherezer and Regemmelech, and their men, to pray before the Lord, And to speak unto the priests which were in the house of the Lord of hosts, and to the prophets, saying, Should I weep in the fifth month, separating myself [NASB, “abstain”], as I have done these so many years?” (Zech. 7:2-3). The Lord’s response stated that it was no longer necessary and therefore needed not to be continued.
In prophetic literature, the verb nâzar indicates Israel’s deliberate separation from Jehovah to dedication of foreign gods or idols. In Hos. 9:10, the various versions differ in their rendering of nâzar: “I found Israel like grapes in the wilderness; I saw your fathers as the firstripe in the fig tree at her first time: but they went to Baal-peor, and separated [NASB, “devoted”; Neb, Rsv “consecrated”] themselves unto that shame; and their abominations were according as they loved.” The prophet Ezekiel employed nâzar: “For every one of the house of Israel, or of the stranger that sojourneth in Israel, which separateth himself from me, and setteth up his idols in his heart, and putteth the stumbling block of his iniquity before his face, and cometh to a prophet to inquire of him concerning me; I the Lord will answer him by myself” (Ezek. 14:7).
Nâzı̂yr ( נָזִר , Strong'S #5139), “one who is separated; Nazarite.” There are 16 occurrences of the word in the Old Testament. The earliest use of nâzı̂yr is found in Gen. 49:26: “The blessings of thy father … shall be on the head of Joseph … that was seperate —from his brethren” (cf. Deut. 33:16). Some modern-speech translators have translated nâzı̂yr in these two verses as “prince” (Niv, Neb, Nab ) The KJV and RSV render the phrase “separate from his brethren.” This interpretation might be justified by assuming that Joseph was separated from his brethren to become the savior of his father, his brethren, and their families.
Most frequently in Old Testament usage, nâzı̂yr is an appellation for one who vowed to refrain from certain things for a period of time: “And this is the law of the Nazarite, when the days of his separation are fulfilled: he shall be brought unto the door of the tabernacle of the congregation” (Num. 6:13).
According to Num. 6, a lay person of either sex could take a special vow of consecration to God’s service for a certain period of time. A “Nazarite” usually made a vow voluntarily; however, in the case of Samson (Judg. 13:5, 7) his parents dedicated him for life. Whether or not this idea of separation to God was distinctive alone to Israel has been debated. Num. 6:1- 23 laid down regulatory laws pertaining to Nazaritism. There were two kinds of “Nazarites”: the temporary and the perpetual. The first class was much more common than the latter kind. From the Bible we have knowledge only of Samson, Samuel, and John the Baptist as persons who were lifelong “Nazarites.”
According to the Mishna, the normal time for keeping a Nazarite vow was thirty days; but sometimes a double vow was taken, lasting sixty days. In fact, a vow was sometimes undertaken for a hundred days.
During the time of his vow, a “Nazarite” was required to abstain from wine and every kind of intoxicating drink. He was also forbidden to cut the hair of his head or to approach a dead body, even that of his nearest relative. If a “Nazarite” accidently defiled himself, he had to undergo certain rites of purification and then had to begin the full period of consecration over again. The “Nazarite” was “holy unto the Lord,” and he wore upon his head a diadem of his consecration.
There is but one reference in the prophetic literature to “Nazarites”: The prophet Amos complained that the Lord had given the Israelites, Nazarites and prophets as spiritual leaders, but that the people “gave the Nazarites wine to drink; and commanded the prophets, saying, Prophesy not” (Amos 2:11-12).
The New Testament occasionally refers to what appear to have been Nazarite vows. For example, Acts 18:18 says that Paul sailed with Priscilla and Aquila, “having shorn his head … for he had a vow” (cf. Acts 21:23-24).
Vine's Expository Dictionary of NT Words 
"to mark off by bounds" (apo, "from," horizo, "to determine;" horos, "a limit"), "to separate," is used of "(a) the Divine action in setting men apart for the work of the gospel, Romans 1:1; Galatians 1:15; (b) the Divine judgment upon men, Matthew 13:49; 25:32; (c) the separation of Christians from unbelievers, Acts 19:9; 2—Corinthians 6:17; (d) the separation of believers by unbelievers, Luke 6:22; (e) the withdrawal of Christians from their brethren, Galatians 2:12 . In (c) is described what the Christian must do, in (d) what he must be prepared to suffer, and in (e) what he must avoid."* [* From Notes on Galatians, by Hogg and Vine, p. 83.]
"to put asunder, separate," is translated "to separate" in Romans 8:35,39; in the Middle Voice, "to separate oneself, depart" (see DEPART); in the Passive Voice in Hebrews 7:26 , Rv , "separated" (AV, "separate"), the verb here relates to the resurrection of Christ, not, as AV indicates, to the fact of His holiness in the days of His flesh; the list is progressive in this respect that the first three qualities apply to His sinlessness, the next to His resurrection, the last to His ascension. See Put , No. 14.
"to mark off" (apo, "from," dia, "asunder," horizo, "to limit"), hence denotes metaphorically to make "separations," Jude 1:19 , RV (AV, "separate themselves"), of persons who make divisions (in contrast with ver. 20); there is no pronoun in the original representing "themselves."
Webster's Dictionary 
(1): ( v. t.) To set apart; to select from among others, as for a special use or service.
(2): ( v. t.) To disunite; to divide; to disconnect; to sever; to part in any manner.
(3): ( v. t.) To come between; to keep apart by occupying the space between; to lie between; as, the Mediterranean Sea separates Europe and Africa.
(4): ( p. a.) Unconnected; not united or associated; distinct; - said of things that have not been connected.
(5): ( v. i.) To part; to become disunited; to be disconnected; to withdraw from one another; as, the family separated.
(6): ( p. a.) Divided from another or others; disjoined; disconnected; separated; - said of things once connected.
(7): ( p. a.) Disunited from the body; disembodied; as, a separate spirit; the separate state of souls.
King James Dictionary 
SEP'ARATE, 5t. L. separo.
1. To disunite to divide to sever to part, in almost any manner, either things naturally or casually joined. The parts of a solid substance may be separated by breaking, cutting or splitting, or by fusion, decomposition or natural dissolution. A compound body may be separated into its constituent parts. Friends may be separated by necessity, and must be separated by death. The prism separates the several kinds of colored rays. A riddle separates the chaff from the grain. 2. To set apart from a number for a particular service.
International Standard Bible Encyclopedia 
sep´a - rā́t : The translation of a number of Hebrew and Greek words, בּדל , bādhal ( Leviticus 20:24 , etc.), and ἀφορίζω , aphorizō ( Matthew 25:32 , etc.), being the most common. "To separate" and "to consecrate" were originally not distinguished (e.g. Numbers 6:2 margin), and probably the majority of the uses of "separate" in English Versions of the Bible connote "to set apart for God." But precisely the same term that is used in this sense may also denote the exact opposite (e.g. the use of nazar in Ezekiel 14:7 and Zechariah 7:3 ). See Holy; Nazirite; Saint .