Fish tooth incomplete (4)
I believe the answer is:
mola
'fish' is the definition.
(mola is a kind of fish)
'tooth incomplete' is the wordplay.
'tooth' becomes 'molar' (molar is a kind of tooth).
'incomplete' means to remove the last letter.
'molar' with its final letter taken away is 'MOLA'.
(Other definitions for mola that I've seen before include "sunfish" , "Panel embroidered by Panama women" .)