Fine long paintbrush (5)

I believe the answer is:

fitch

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

'paintbrush' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

'fine long' is the wordplay.
'fine' becomes 'f' (abbreviation).
'long' becomes 'itch' (to long or itch for something is to desire it).
'f'+'itch'='FITCH'

Can you help me to learn more?

(Another definition for fitch that I've seen is " Polecat fur".)

I've seen this clue in the Sydney Morning Herald.

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