Undergarment on a goddess (5)
I believe the answer is:
vesta
'goddess' is the definition.
(I have seen 'Roman goddess ' mean 'vesta' so perhaps 'goddess' could also mean 'vesta')
'undergarment on a' is the wordplay.
'undergarment' becomes 'vest' (vest is a kind of undergarment).
'on' says to put letters next to each other.
'vest'+'a'='VESTA'
(Other definitions for vesta that I've seen before include "heavenly body" , "Roman goddess; match" , "Asteroid; goddess; match" , "Roman goddess of the hearth" , "Stave (anag.)" .)