present participle of on

(idiomatic) To misspeak, to say something embarrassing or wrong, or to make a mistake in public, or a social blunder, that is embarrassing or offensive.

The state of having invested heavily in just one area. / The state of having devoted all of one’s resources to one thing.

(idiomatic) To remain calm, composed, focused, or aware.

Alternative form of wear one's heart on one's sleeve

Alternative form of keep one's head

Alternative form of wear one's heart on one's sleeve

Alternative form of have one's wits about one

(literally) To direct a horse to walk, canter, trot, etc. / (idiomatic) To test several or all functions or training of a person, animal, machine, etc.

Said of something that can be done very easily.