Right to avoid fireplace opening (4)
I believe the answer is:
gate
'opening' is the definition.
(a gate is an opening or entrance)
'right to avoid fireplace' is the wordplay.
'right' becomes 'r' (abbreviation).
'to avoid' suggests deleting specific letters.
'fireplace' becomes 'grate' (grate can mean a fireplace).
'grate' with 'r' removed is 'GATE'.
(Other definitions for gate that I've seen before include "Attendance; entrance" , "Entry to arena" , "Barrier - door" , "Plane-boarding point" , "Spectators - entrance" .)