Component of a certain cage (3)
I believe the answer is:
rib
'component of a certain cage' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rib that I've seen before include "Vein structure in a leaf" , "Poke fun at the bone" , "Tease good-naturedly" , "Tease; body part" , "Supporting structure" .)