Only in two words (7,3)

I believe the answer is:

nothing but

I'm a little stuck... Click here to teach me more about this clue!

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

'in two words' is the wordplay.
I cannot really see how this works, but
'in' is present in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

(Another definition for nothing but that I've seen is " only".)

I've seen this clue in the Evening Standard.

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