Unusually speechless actor (5)

I believe the answer is:

extra

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This clue could be a double definition.

'unusually' is the first definition.
(extra can mean to an unusual degree)

'speechless actor' is the second definition.
'extra' can be an answer for 'actor' (extra is a type of actor). I am not sure about the 'speechless' bit.

Can you help me to learn more?

(Other definitions for extra that I've seen before include "Minor actor in crowd scenes" , "Surplus to requirements" , "Left over" , "Small part actor" , "Minor actors in crowd scenes" .)

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

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