Animal left at the waterside (4)
I believe the answer is:
seal
'the waterside' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'animal left' is the wordplay.
'animal' becomes 'sea' (sea animal is a kind of animal).
'left' becomes 'L' (common abbreviation).
'sea'+'l'='SEAL'
'at' is the link.
Can you help me to learn more?
(Other definitions for seal that I've seen before include "Stamp of approval" , "Close - (performing?) animal" , "Close up - marine mammal" , "Stamp of guarantee" , "Marine animal or sign of authenticity" .)