Mouthful of water (7)
This could be a double definition.
'mouthful' is the first definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'water' is the second definition.
(I know that estuary is a type of water)
'of' acts as a link.
Can you help me to learn more?
(Other definitions for estuary that I've seen before include "form of English" , "route to sea" , "Weapon" , "Wide river mouth" , "A surety found in river's tidal mouth" .)
'mouthful of water' is the definition.
The answer and definition can be both natural objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
This is the entire clue.
Can you help me to learn more?
(Other definitions for delta that I've seen before include "Type of wing" , "Triangular river system" , "Multiple estuary" , "Area of distributaries at a river mouth" , "Triangular patch of land at mouth of river" .)