num. one —see Oon
no.Costermongers' Back Slang.

On est un sot = “They-say-so” is half a liar.

[Note that there is no liaison after On here.]

prep. on, at, in, among, ofVariants: one, onne, a,o,an, Etymology: Anglo-Saxon an, on

on is frequently used where in would be preferable. Fitz-Greene Halleck once said to a friend, “Why do people persist in saying on Broadway? Might they not as well say Our Father, who art on Heaven?”

“to be on ,” in public-house or vulgar parlance, is synonymous with getting “tight” or tipsy; “it's St. Monday with him, I see he's on  again,” i.e., drunk as usual, or on the road to it. “I'm on ” also expresses a person's acceptance of an offered bet. To get on  a horse or a man is to make bets on it or him. “Try it on ,” a defiant challenge to a person.