Passage I seal off (5)
I believe the answer is:
aisle
'passage' is the definition.
(aisle can mean a path or passageway)
'i seal off' is the wordplay.
'off' indicates anagramming the letters.
'i'+'seal'='iseal'
'iseal' is an anagram of 'AISLE'.
(Other definitions for aisle that I've seen before include "Corridor" , "Passages between seating areas" , "Division of the nave in church" , "lateral strip" , "Extension of the nave in a church" .)