Widespread agitating I’d suffer endlessly (7)
I believe the answer is:
diffuse
'widespread' is the definition.
(thesaurus)
'agitating i'd suffer endlessly' is the wordplay.
'agitating' indicates anagramming the letters.
'endlessly' means to remove the last letter.
'id'+'suffer'='idsuffer'
'idsuffer' with its final letter taken away is 'idsuffe'.
'idsuffe' is an anagram of 'DIFFUSE'.
(Other definitions for diffuse that I've seen before include "Without concentration" , "Widely spread" , "Radiate; unfocused" , "Spread out, not concentrated" , "Circumlocutory" .)