The first man lacks a mother (3)
I believe the answer is:
dam
'mother' is the definition.
(female parent of an animal)
'the first man lacks a' is the wordplay.
'the first man' becomes 'adam' (first man in the Bible).
'lacks' is a deletion indicator.
'adam' with 'a' removed is 'DAM'.
(Other definitions for dam that I've seen before include "Female parent of an animal, especially livestock" , "River restraint" , "Female parent; obstruction" , "eg Aswan" , "Barrier to contain the flow of water" .)