siditty etymology? BE for feeling superior(1967)

[Cohen, Gerald Leonard]

FWIW, there are two other BE terms for "snobbish, stuck-up, full of airs,"
and they too are of unknown origin:

"dicty" (first attestation 1923)
"hincty" (also = suspicious)--first attestation: 1924.
See HDAS. Also, Clarence Major's _Juba to Jive_ has "seddity" = bourgeois black person; snobbish and pretentious."

So: dicty, hincty, siddity/seditty.  The pattern seems to be telling us something, but what?   Btw, any chance that "hincty" might derive from French "inquiété" (worried )?  A black person overly worried about what white folks might think about his/her actions/speech/ etc. might be viewed as
snobbish by fellow blacks. And "worried" would also lead  easily to the second meaning of "hincty," viz. "suspicious."

Gerald Cohen