Coffee, second of two, unfinished (5)
I believe the answer is:
latte
'coffee' is the definition.
(I've seen this before)
'second of two unfinished' is the wordplay.
'second of two' becomes 'latter' (I've seen this before).
'unfinished' means to remove the last letter.
'latter' with its final letter taken off is 'LATTE'.
(Other definitions for latte that I've seen before include "Italian word for milk" , "Milky coffee drink" , "coffee production" , "See 21" , "hot drink" .)