Diver’s remorse, eating endless acidic fruit (9)
I believe the answer is:
guillemot
'diver's' is the definition.
(I've seen this before)
'remorse eating endless acidic fruit' is the wordplay.
'remorse' becomes 'guilt' (guilt is a kind of remorse).
'eating' is an insertion indicator.
'endless' means to remove the last letter.
'acidic fruit' becomes 'lemon' (I've seen this before).
'lemon' with its final letter taken off is 'lemo'.
'guilt' placed around 'lemo' is 'GUILLEMOT'.
(Other definitions for guillemot that I've seen before include "An auk" , "Fisher" , "Diving bird" , "Seabird" , "Diver" .)