Alternative theatre is most indecent (9)

I believe the answer is:

earthiest

'most indecent' is the definition.
('earthy' can be similar in meaning to 'indecent')

'alternative theatre is' is the wordplay.
'alternative' indicates an anagram (an alternative ordering of the letters).
'theatre'+'is'='theatreis'
'theatreis' is an anagram of 'EARTHIEST'.

(Another definition for earthiest that I've seen is " The most coarse".)

I've seen this clue in The Guardian.

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