Definition of "conspiratorial"

I pressed the button and he appeared, giving me, as he entered, the sort of conspiratorial glance the acting secretary of a secret society would have given a friend on the membership roll. “Oh, Swordfish,” I said, having given him a conspiratorial glance in return, for one always likes to do the civil thing, “this is Mr Herring, who has come to join our little group.”

1960, P[elham] G[renville] Wodehouse, chapter X, in Jeeves in the Offing, London: Herbert Jenkins

Conspiratorial thinking is another predictor of vaccine hesitancy, according to the 2018 study.

2021 April 29, Sabrina Tavernise, “Vaccine Skepticism Was Viewed as a Knowledge Problem. It’s Actually About Gut Beliefs.”, in The New York Times‎, New York, N.Y.: The New York Times Company, archived from the original on 2021-04-29