Essential feature of theme's called for an intoxicant (6)

I believe the answer is:

mescal

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'an intoxicant' is the definition.
(mescal is a kind of intoxicant)

'essential feature of theme's called' is the wordplay.
'MESCAL' is hidden within the letters.
However, I'm unsure how the hidden word is indicated.

'for' is the link.

Can you help me to learn more?

(Other definitions for mescal that I've seen before include "Intoxicant from agave" , "Colourless Mexican spirit made from plant sap" , "Drink distilled from agave" .)

I've seen this clue in The Independent.

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