"square" = "dull, rigidly conventional"

[Joel S. Berson]

Does the sense "square" = "conventional, old-fashioned" (from 1946)
derive from "square peg (in a round hole)"?  (The OED has variants of
this from 1836.)  Or from the sense "Just or equitable; fair, honest,
honourable, straightforward" (from around 1600) becoming "overly
..."?  Or from something else?

Joel

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