Large cup for a small mouth? (6)
I believe the answer is:
goblet
This clue could be a double definition.
'large cup' is the first definition.
'goblet' can be an answer for 'cup' (I've seen this before). I'm not sure about the 'large' bit.
'small mouth?' is the second definition.
(goblet could whimsically mean a small gob or mouth)
'for a' acts as a link.
Can you help me to learn more?
(Other definitions for goblet that I've seen before include "Large drinking cup" , "Bowl-shaped drinking vessel" , "small mouth?" , "Drinking-glass with stem and foot" , "Chalice" .)