Loan left to finish (4)
I believe the answer is:
lend
'loan' is the definition.
(I know that loan can be written as lend)
'left to finish' is the wordplay.
'left' becomes 'l' (common abbreviation).
'to finish' becomes 'end' (synonyms).
'l'+'end'='LEND'
(Other definitions for lend that I've seen before include "Give the use of for a time" , "Make a loan" , "Impart" , "Give temporarily" , "Let someone borrow" .)