Adam and Eve's third son (4)
I believe the answer is:
seth
'adam and eve's third son' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for seth that I've seen before include "Early man" , "god of Egypt" , "Adam and Eve's third child" , "In disguise, the brother of Cain and Abel" , "Biblical character" .)