Catch an apprentice helping to make varnish! (5)

I believe the answer is:

copal

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'helping to make varnish' is the definition.
I can't tell whether this definition defines the answer.

'catch an apprentice' is the wordplay.
'catch' becomes 'cop' (I've seen this before).
'an' becomes 'a'.
'apprentice' becomes 'l' (abbreviation for 'Learner').
'cop'+'a'+'l'='COPAL'

Can you help me to learn more?

(Other definitions for copal that I've seen before include "Resin used in varnish" , "Aromatic tree resin" , "Hard resin" .)

I've seen this clue in the Evening Standard.

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