A voice of regal tone (4)

I believe the answer is:

alto

'a voice' is the definition.
(alto is a kind of voice)

'of regal tone' is the wordplay.
'of' indicates a hidden word.
'ALTO' can be found hidden inside 'regal tone'.

(Other definitions for alto that I've seen before include "Male singer" , "Low female singing voice" , "Unisex vocal range" , "Member of choir" , "Key old > male who scores high" .)

I've seen this clue in the Evening Standard.

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