Cat snore irritated forefather (8)
I believe the answer is:
ancestor
'forefather' is the definition.
(I've seen this before)
'cat snore irritated' is the wordplay.
'irritated' indicates an anagram (I've seen this in other clues).
'cat'+'snore'='catsnore'
'catsnore' with letters rearranged gives 'ANCESTOR'.
(Other definitions for ancestor that I've seen before include "An escort (anag.)" , "not being of the modern generation" , "One of one's forebears" , "Adam was our first one" , "Person from whom one is descended" .)