It sounds highly unnatural (8)

I believe the answer is:

falsetto

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'it sounds highly unnatural' is the definition.
The definition suggests a singular noun which matches the answer.

This is the entire clue.

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(Other definitions for falsetto that I've seen before include "High singing method" , "Voice one's raised" , "Aritifical upper register of male voice" , "High-pitched male voice" , "Unusually high voice" .)

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

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