Wise man endlessly to wilt (3)
I believe the answer is:
sag
'wilt' is the definition.
(thesaurus)
'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 last letter taken away is 'SAG'.
'to' is the link.
(Other definitions for sag that I've seen before include "Sink under weight" , "Cave in" , "Droop, flag" , "Droop, sink in the middle" , "Decline" .)