A short waistcoat intended to serve as a robe (8)
I believe the answer is:
vestment
'robe' is the definition.
(I know that vestment is a type of robe)
'a short waistcoat intended to serve as a' is the wordplay.
I cannot quite see how this works, but
'waistcoat' could be 'vest' (synonyms) and 'vest' is found in the answer.
The remaining letters 'ment' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for vestment that I've seen before include "Priestly garment" , "Religious garment" , "A minister assumes this" , "Clerical robe" , "What clergyman puts on" .)