Forbear to check out the RAF activity (7)
I believe the answer is:
refrain
'forbear' is the definition.
(synonyms)
'check out the raf activity' is the wordplay.
'check' becomes 'rein' (both can mean to control or limit).
'out' means one lot of letters goes inside another.
'activity' is an anagram indicator (letters become active).
'raf' is an anagram of 'fra'.
'rein' enclosing 'fra' is 'REFRAIN'.
'to' is the link.
(Other definitions for refrain that I've seen before include "burden" , "Chorus; keep away (from)" , "Stop activity" , "Forbear from chorus?" , "Stop oneself (from doing something)" .)