Can be bitten, though cutting is appropriate (4)

I believe the answer is:

tart

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'appropriate' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for tart that I've seen before include "Biting - pastry" , "Astringent" , "A bit sour like open cake" , "Open-topped pie" , "Sour-tasting pie?" .)

I've seen this clue in the Evening Standard.

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