Check before opening (7)
I believe the answer is:
prevent
'check' is the definition.
(thesaurus)
'before opening' is the wordplay.
'before' becomes 'pre'.
'opening' becomes 'vent' (vent is a kind of opening**).
'pre'+'vent'='PREVENT'
(Other definitions for prevent that I've seen before include "Keep from happening" , "Avert, hinder" , "Stop, hinder" , "Keep from arising" , "Stop (an action)" .)