At home, allow vent (5)
I believe the answer is:
inlet
'vent' is the definition.
(thesaurus)
'at home allow' is the wordplay.
'at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'allow' becomes 'let' (synonyms).
'in'+'let'='INLET'
(Other definitions for inlet that I've seen before include "Bay or recess" , "Small opening of coastline" , "A small creek or cove" , "Bay, bight" , "Narrow arm of water" .)