Traditionalist, one of a number on the board? (6)

I believe the answer is:

square

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

'traditionalist' is the definition.
(both can mean a boring or traditionalist person)

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for square that I've seen before include "Bribe" , "Plane figure" , "Level - shape - piazza - stuffy" , "Chess board unit" , "See 6" .)

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app