Strain to keep from (7)
I believe the answer is:
refrain
I believe this clue is a double definition.
'strain' is the first definition.
(thesaurus)
'keep from' is the second definition.
(thesaurus)
'to' acts as a link.
(Other definitions for refrain that I've seen before include "Main part of song - do not do it" , "Chorus of a song" , "Main theme" , "Stop activity" , "Much repeated saying" .)