From BiblePortal Wikipedia

Fausset's Bible Dictionary [1]

Condensing in one emphatic syllable all that is implied in Jahveh (or Υahweh ), the true pronunciation of Jehovah ( Psalms 68:4); first in  Exodus 15:2 (Hebrew). Often in names, as Εli-Jah . Only in poetry:  Isaiah 12:2, " Jah (or Υah ) Jehovah is my strength and my song"; ( Isaiah 26:4) "in Jah (or Υah ) Jehovah is the Rock of ages." The union of the two names expresses in the highest degree God's unchanging love and power. Ηallelu-Jah (or Ηallelu-Υah ) is "Praise ye Jah (or Υah )".  Psalms 89:8, "O Jehovah , God of hosts, who, as Thou, is a strong Jah (or Υah )?" the emphatic concentration of the name "Jehovah." The spirit impressed with a sense of God feels the need of repeating frequently that name in which His being is comprehended (Hengstenberg).

Smith's Bible Dictionary [2]

Jah. (Jehovah). The abbreviated form of Jehovah , used only in poetry. It occurs frequently in the Hebrew, but with a single exception,  Psalms 68:4, is rendered "Lord" in the Authorized Version. The identity of Jah and Jehovah is strongly marked in two passages of Isaiah -  Isaiah 12:2;  Isaiah 26:4. See Jehovah .

Hawker's Poor Man's Concordance And Dictionary [3]

One of the glorious incommunicable names of JEHOVAH. We find it joined with many Hebrew names in the Scripture. The grand Anthem hymn is called Hallel-Jah, praise the Lord, which we pronounce Hallelujah. So again, when speaking of JEHOVAH in his covenant-relation in Christ, we say Adon Jah, or Adoni, my Adoni Jah. And hence the Hebrews were so fond of calling their children by some name that took in and comprehended somewhat of this name. Thus Isaiah, Jeremiah, Zephaniah, Zechariah, etc.

See Jehovah

People's Dictionary of the Bible [4]

Jah ( Jäh ).  Psalms 68:4. A form of the Hebrew word "Jehovah." It is part of the compound words "Adonijah" ("God is my Lord") and "hallelujah" ("Praise the Lord"). See Jehovah.

Watson's Biblical & Theological Dictionary [5]

one of the names of God, which we meet with in the composition of many Hebrew words; as, Adonijah, Allelujah, Malachia; that is, "My Lord," "Praise the Lord," "The Lord is my King."

Morrish Bible Dictionary [6]

An abbreviated form of Jehovah.  Psalm 68:4 . The same Hebrew word occurs many times, and is translated LORD. See GOD.

American Tract Society Bible Dictionary [7]

A Hebrew contraction for  Psalm 68:4 . It is often found in Hebrew compound words, as in Adonijah, Malachia, Hallelujah.

Holman Bible Dictionary [8]

 Psalm 68:4God

Hastings' Dictionary of the Bible [9]

JAH . See God, § 2 ( g ).

Easton's Bible Dictionary [10]

 Psalm 68:4

King James Dictionary [11]

JAH, n. Jehovah.

Webster's Dictionary [12]

(n.) Jehovah.

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [13]

(Heb. Yah, יָהּ , a contraction for יַהוָֹה , Jehovah,  Psalms 68:4, elsewhere rendered "Lord"). (See Jehovah); (See Hallelujah). It also enters into the composition of many Heb. names, as Adonijah, Isaiah etc.