(idiomatic) At one's own instigation, of one's own accord.

(idiomatic, nautical) About to be married.

Atop / Very close to, in any orientation or in time. / (idiomatic) In addition to something else. / (idiomatic) Fully informed about, and in control of, something; up to speed with.

Alternative spelling of on demand

(idiomatic) Honest(ly), sincere(ly), straightforward(ly), fair(ly). / Synonym of on the square (“discreet reference to freemasonry”)

(US, idiomatic) After reconsidering; on further consideration.

(idiomatic) Unwillingly agreed to or barely tolerated.

A spectator; someone looks on or watches, without becoming involved or participating.

(idiomatic) On one's hands and knees. / (idiomatic, often followed by "with") In a manner which is similar in nature or effect to something else; consistently.

Alternative form of in heat