Expert, virtuoso (6)

I believe the answer is:

master

I believe this clue is a double definition.

'expert' is the first definition.
(I know that master is a type of authority)

'virtuoso' is the second definition.
(I've seen this before)

(Other definitions for master that I've seen before include "With 1a [OLD], one who painted" , "Gain control of (something)" , "get control over" , "Virtuoso" , "Teacher to gain control" .)

I've seen this clue in The Times.

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