Finish nothing with supply (5)
I believe the answer is:
endow
'supply' is the definition.
(I've seen this before)
'finish nothing with' is the wordplay.
'finish' becomes 'end' (synonyms).
'nothing' becomes 'O' (looks like zero - 0).
'with' becomes 'w' (short for with).
'end'+'o'+'w'='ENDOW'
(Other definitions for endow that I've seen before include "Give qualities or abilities to" , "Provide (with financial support, qualities etc)" , "Attribute abilities to" , "Bestow" , "Enrich (with a facility or gift)" .)