A most unusual surgical opening (5)

I believe the answer is:

stoma

'surgical opening' is the definition.
(I've seen this before)

'a most unusual' is the wordplay.
'unusual' indicates an anagram.
'a'+'most'='amost'
'amost' anagrammed gives 'STOMA'.

(Other definitions for stoma that I've seen before include "surgical opening" , "Pore in plant" .)

I've seen this clue in The Globe and Mail.

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