Crossword Genius

In short, brilliant! (3)

Ross

I believe the answer is:

fab

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

This clue could be a double definition.

'in' is the first definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?

'short brilliant' is the second definition.
(short for fabulous; 'short' asks for a short form)

Can you help me to learn more?

(Other definitions for fab that I've seen before include "Excellent (slang)" , "Marvellous (sl.)" .)

I've seen this clue in the Evening Standard.
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