Only a companion, yet apt to be aggressive (5)

I believe the answer is:

butch

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'apt to be aggressive' is the definition.
I can't judge whether this defines the answer.

'only a companion' is the wordplay.
'only' becomes 'but' (but can mean only - eg 'life is but a dream').
'a companion' becomes 'ch' (Companion of Honour).
'but'+'ch'='BUTCH'

'yet' acts as a link.

Can you help me to learn more?

(Other definitions for butch that I've seen before include "Aggressively masculine" , "Tough" , "Acting as a male (colloq.)" , "Markedly masculine" , "Macho" .)

I've seen this clue in the Evening Standard.

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