From BiblePortal Wikipedia

Vine's Expository Dictionary of OT Words [1]

A. Noun.

Mâchâr ( מָחָר , Strong'S #4279), “tomorrow.” This word has cognates in late Aramaic, Egyptian, Syriac, Phoenician, and Akkadian (here it appears with the word for “day”). Mâchâr appears as a noun or an adverb about 52 times in biblical Hebrew and in all periods of the language.

The word means the day following the present day: “… Tomorrow is the rest of the holy sabbath unto the Lord: bake that which ye will bake today …” (Exod. 16:23). Mâchâr also occurs as a noun in Prov. 27:1: “Boast not thyself of tomorrow; for thou knowest not what a day may bring forth.”

B. Adverbs.

Mâchâr ( מָחָר , Strong'S #4279), “tomorrow.” The basic meaning of this word is clearly set forth in Exod. 19:10: “And the Lord said unto Moses, Go unto the people, and sanctify them today and tomorrow, and let them wash their clothes.” In a few passages the Akkadian idiom is closely paralleled—the phrase yom mâchâr —is used: “So shall my righteousness answer for me in time to come [later] …” (Gen. 30:33). In most passages mâchâr by itself (used absolutely) means “tomorrow”: “Behold, I go out from thee, and I will entreat the Lord that the swarms of flies may depart from Pharaoh, from his servants, and from his people, tomorrow …” (Exod. 8:29). Interestingly, in Exod. 8:10 the phrase lemâchâr —(which appears 5 times in the Bible) is used: “And he said, Tomorrow.” Used with the preposition ke , the word means “tomorrow about this time”: “Behold, tomorrow about this time I will cause it to rain a very grievous hail …” (Exod. 9:18).

Mochŏrâth ( מָחֳרָתָם , Strong'S #4283), “the next day.” Closely related to the noun mochŏrâth is this adverb, which occurs about 32 times and in all periods of biblical Hebrew. About 28 times mochŏrâth is joined to the preposition min to mean “on the next day.” This is its form and meaning in its first biblical appearance: “And it came to pass on the morrow …” (Gen. 19:34). In 3 passages this adverb is preceded by the preposition le , but the meaning is the same: “And David smote them from the twilight even unto the evening of the next day …” (1 Sam. 30:17). In Num. 11:32 mochŏrâth appears after yom , “day,” and is preceded by the definite article: “And the people stood up all that day, and all that night, and all the next day, and they gathered the quails.…” First Chron. 29:21 displays yet another construction, with the same meaning: “… On the morrow after that day.…”

C. Verb.

‘Achar means “to be behind, tarry, defer.” This verb, which occurs rarely in biblical Hebrew, is usually considered the root of machar , “tomorrow.” This verb appears in Prov. 23:30: “They that tarry long at the wine; they that go to seek mixed wine.” The meaning of “to tarry” also occurs in Judg. 5:28: “Why tarry the wheels of his chariots?”

Vine's Expository Dictionary of NT Words [2]

1: Αὔριον (Strong'S #839 — Adverb — aurion — ow'-ree-on )

is used either without the article, e.g.,  Matthew 6:30;  1—Corinthians 15:32;  James 4:13; or with the article in the feminine form, to agree with hemera, "day," e.g.,  Matthew 6:34;  Acts 4:3 , RV, "the morrow" (AV, "next day");  James 4:14; preceded by epi, "on," e.g.,  Luke 10:35;  Acts 4:5 .

Webster's Dictionary [3]

(1): ( n.) The day after the present; the morrow.

(2): ( adv.) On the day after the present day; on the next day; on the morrow.