Left to finish loan (4)
I believe the answer is:
lend
'loan' is the definition.
('lend' can be a synonym of 'loan')
'left to finish' is the wordplay.
'left' becomes 'l' (common abbreviation).
'to finish' becomes 'end' ('end' can be a synonym of 'finish').
'l'+'end'='LEND'
(Other definitions for lend that I've seen before include "Give on condition of return" , "contribute" , "Give the use of for a time" , "Advance, loan" , "Give (a quality) to" .)