Wise man endlessly to wilt (3)
I believe the answer is:
sag
'wilt' is the definition.
(I've seen this in another clue)
'wise man endlessly' is the wordplay.
'wise man' becomes 'sage' (sage is a kind of wise man).
'endlessly' means to remove the last letter.
'sage' with its final letter taken off is 'SAG'.
'to' acts as a link.
(Other definitions for sag that I've seen before include "Sink under weight" , "Cave in" , "Droop, flag" , "Droop, sink in the middle" , "Decline" .)