One headed for sack after abusing terrier (7)
I believe the answer is:
retirer
'one headed for sack' is the definition.
The definition suggests a singular noun which matches the answer.
'abusing terrier' is the wordplay.
'abusing' indicates anagramming the letters (I've seen 'abused' mean this).
'terrier' is an anagram of 'RETIRER'.
'after' is the link.
Can you help me to learn more?
(Other definitions for retirer that I've seen before include "he goes to bed" , "One going to bed" .)