Crossword Genius

Small argument was formal (5)

Ross

I believe the answer is:

stiff

'formal' is the definition.
(similar in meaning)

'small argument' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'argument' becomes 'tiff' (I've seen this in other clues).
's'+'tiff'='STIFF'

'was' acts as a link.

(Other definitions for stiff that I've seen before include "18 [HARD]" , "cheat" , "One dead" , "Rigid, unbending" , "Starched, rigid" .)

I've seen this clue in The Mirror.
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