Brewer's: Sit Upon
(To). To snub, squash, smother, set down; the Latin insideo. Charlotte Brontë, in Shirley (xxviii.), uses a phrase which seems analagous: Miss Keeldar says she mentioned the mischance to no one- “I preferred to cushion the matter.”
“Mr. Schwann and his congeners should be most energetically sat upon by colleagues and opponents alike, by everyone, in fact, who has the welfare of the empire at heart.” —The World, April 6th, 1892, p. 19.