Wear a sort of square flag (6)

I believe the answer is:

attire

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

'a sort of square flag' is the wordplay.
'sort of square' becomes 't' (a T-Square is a technical drawing instrument).
'flag' becomes 'tire' (I've seen this before).
'a'+'t'+'tire'='ATTIRE'

(Other definitions for attire that I've seen before include "Clothing, apparel" , "Fine/formal clothes" , "Wear" , "Formal clothes" , "Formal clothing" .)

I've seen this clue in The Times.

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