Leave vet interminably holding a pet (6)
I believe the answer is:
vacate
'leave' is the definition.
(to vacate a place is to leave it)
'vet interminably holding a pet' is the wordplay.
'interminably' means to remove the last letter.
'holding' indicates putting letters inside.
'pet' becomes 'cat' (I have seen 'Common pet ' mean 'cat' so perhaps 'pet' could also mean 'cat').
'vet' with its last letter removed is 've'.
'a'+'cat'='acat'
've' placed around 'acat' is 'VACATE'.
(Other definitions for vacate that I've seen before include "Make empty" , "Depart from, leave empty" , "Caveat - cease to occupy" , "Leave behind empty" , "Quit" .)