Vault part (3)
I believe the answer is:
rib
'vault part' 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 "knitting pattern" , "Eve is knownj as Adam's . . ." , "Tease; body part" , "One of 12 pairs of curved bones" , "Kid" .)