Stagger to us and collapse (7)
I believe the answer is:
astound
'stagger' is the definition.
(thesaurus)
'to us and collapse' is the wordplay.
'collapse' indicates an anagram.
'to'+'us'+'and'='tousand'
'tousand' anagrammed gives 'ASTOUND'.
(Other definitions for astound that I've seen before include "Shock, surprise greatly" , "Stupefy" , "Fill with wonder or astonishment" , "floor" , "Shock - amaze" .)