Little beast, a bit of a crook (3)

I believe the answer is:

roo

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

'little beast' is the definition.
The definition suggests a singular noun which matches the answer.

'a bit of a crook' is the wordplay.
'a bit of' indicates the answer is hidden within the clue.
'ROO' is hidden within 'crook'.

Can you help me to learn more?

(Other definitions for roo that I've seen before include "Young marsupial" , "Marsupial (informal)" , "Kangaroo (Austr. colloq.)" , "Wild animal" , "Diminutive inhabitant of Hundred Acre Wood" .)

I've seen this clue in the Evening Standard.

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