Vessel's tiny mouth? (6)
I believe the answer is:
goblet
'vessel's' is the definition.
(thesaurus)
'tiny mouth?' is the wordplay.
I cannot quite see how this works, but
'mouth?' could be 'gob' (informal term for the mouth) and 'gob' is present in the answer.
The remaining letters 'let' 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 goblet that I've seen before include "Large drinking cup" , "Large handleless drinking-cup" , "Bowl-shaped drinking vessel" , "small mouth?" , "Drinking-glass with stem and foot" .)