From BiblePortal Wikipedia

Smith's Bible Dictionary [1]

Methu'sael. (Man Of God). The son of Mehujael, fourth in descent from Cain, and father of Lamech.  Genesis 4:18.

Holman Bible Dictionary [2]

 Genesis 4:18 Genesis 5:21

Fausset's Bible Dictionary [3]

Son of Mehujael in Cain's line, and Lamech's father ( Genesis 4:18).

Morrish Bible Dictionary [4]

Son of Mehujael and father of Lamech.  Genesis 4:18 .

Easton's Bible Dictionary [5]

 Genesis 4:18

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [6]

(Hebrews Methushatl', מְתוּשָׁאֵל , Man That is from God; Sept. Μαθουσάλα , Vulg. Mathusael ), the son of Mehujael and father of Lamech, of the family of Cain ( Genesis 4:18). BC. cir. 3770. The resemblance of the name to the following, on which (with the coincidence of the name Lamech in the next generation in both lines) some theories have been formed, is apparent rather than real.

Kitto's Popular Cyclopedia of Biblial Literature [7]

Methu´sael (man of God), son of Mehujael, of the race of Cain .