Crossword Genius

Little monkey’s spotted leaving river (3)

Ross

I believe the answer is:

imp

I'm a little stuck... Click here to teach me more about this clue!

This might be a double definition.

'little monkey's' is the first definition.
(thesaurus)

'leaving river' is the second definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'spotted' acts as a link.

Can you help me to learn more?

(Other definitions for imp that I've seen before include "Goblin" , "little chap" , "puck" , "old-fashioned graft" , "Wicked spirit" .)

I've seen this clue in The Times.
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