Pair outside happening to stop (7)
I believe the answer is:
prevent
'stop' is the definition.
(thesaurus)
'pair outside happening' is the wordplay.
'outside' means to remove the middle letters.
'happening' becomes 'event' (I've seen this before).
'pair' with its centre taken out is 'pr'.
'pr'+'event'='PREVENT'
'to' is the link.
(Other definitions for prevent that I've seen before include "Stop, hinder" , "Stop, avert" , "Avert, hinder" , "Keep from arising" , "Keep from happening" .)