Biblical character slaughtered lamb as first of offerings (7)
I believe the answer is:
absalom
'biblical character' is the definition.
(Absalom matches up with the definition biblical character)
'slaughtered lamb as first of offerings' is the wordplay.
'slaughtered' indicates an anagram.
'first of offerings' becomes 'o' (1st letter of 'offerings').
'lamb'+'as'+'o'='lambaso'
'lambaso' anagrammed gives 'ABSALOM'.
(Other definitions for absalom that I've seen before include "King's rebellious son" , "David's boy" , "Son of King David (Bible)" , "Son of King David (OT)" , "David's third son (OT)" .)