A topless specimen is quite enough (5)
I believe the answer is:
ample
'quite enough' is the definition.
(I've seen this before)
'a topless specimen' is the wordplay.
'a topless' means to remove the first letter.
'specimen' becomes 'sample' (I've seen this before).
'sample' with its initial letter removed is 'AMPLE'.
'is' acts as a link.
(Other definitions for ample that I've seen before include "Bulky" , "Plenty, more than enough" , "Plenteous" , "Buxom" , "Easily sufficient" .)