Simply unique (4)

I believe the answer is:

only

I believe this is a double definition.

'simply' is the first definition.
('only' can be a synonym of 'simply')

'unique' is the second definition.
('only' can be a synonym of 'unique')

(Other definitions for only that I've seen before include "Existing alone with no other, perhaps a child" , "Except that; single" , ". . . . the Lonely (sung by Roy Orbison)" , "Simply" , "Solely, lone" .)

I've seen this clue in The Telegraph.

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