Rib about ‘big trap’ occasionally (5)
I believe the answer is:
costa
'rib' is the definition.
(synonyms)
'about big trap occasionally' is the wordplay.
'about' becomes 'c' (circa).
'big' becomes 'os' (abbreviation for oversize).
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
The alternating letters of 'trap' are 'ta'.
'c'+'os'+'ta'='COSTA'
(Other definitions for costa that I've seen before include "and 5 Down: Spanish holiday destination" , "A Spanish coast, may be Del Sol" , "resort abroad" , "Rib or rib-like structure" , "-- Brava; -- Blanca" .)