Biblical father of Jacob (5)
I believe the answer is:
isaac
'biblical father of jacob' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for isaac that I've seen before include "Jewish name?" , "-- Asimov, science fiction writer" , "Son prepared for sacrifice" , "___ Newton, English physicist, d. 1727" , "Father of 21" .)