Instruct in art? (5)

I believe the answer is:

train

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

'instruct' is the definition.
(I know that train is a type of instruct)

'in art?' is the wordplay.
'in art' anagrams to 'TRAIN'.
But, I'm not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for train that I've seen before include "Form of transport" , "Learn a skill etc. through practice" , "Line of carriages with a locomotive" , "Groom" , "Long back section of a gown that's drawn along the floor" .)

I've seen this clue in the Evening Standard.

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