Tail of squirrel monkey hanging down (4)
I believe the answer is:
limp
'hanging down' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'tail of squirrel monkey' is the wordplay.
'tail of' indicates one should take the final letters.
'monkey' becomes 'imp' (synonyms).
The last letter of 'squirrel' is 'l'.
'l'+'imp'='LIMP'
Can you help me to learn more?
(Other definitions for limp that I've seen before include "Walk with an uneven stop" , "Floppy" , "Walk with difficulty" , "exhausted" , "Feeble" .)