Small lake would be more than enough for this sailor (3)
I believe the answer is:
tar
'this sailor' is the definition.
(slang term for a sailor)
'small lake would be more than enough for' is the wordplay.
'small lake' becomes 'tarn' (term for a mountain lake).
'would be more than enough for' means to remove the last letter (the word has more letters than are needed).
'tarn' with its last letter taken off is 'TAR'.
(Other definitions for tar that I've seen before include "A sailor; a preservative" , "Sticky cigarette residue" , "Road-dressing for a sailor?" , "Familiar sailor - what a rat" , "Informal sailor or road surfacing material" .)