It may well hold water (4)
I believe the answer is:
ewer
This could be a double definition.
'it' is the first definition.
The definition suggests a singular noun which matches the answer.
'well hold water' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'may' acts as a link.
Can you help me to learn more?
(Other definitions for ewer that I've seen before include "Large water-jug" , "Decorative pitcher" , "Open vessel with handle and spout" , "Were (anag)" , "Large pitcher" .)