The underside of an animal. / The underside of any thing. / (figuratively) The side which is not normally seen, normally a dark, immoral place.

(idiomatic) Whose future is uncertain due to an anticipated threat or change in circumstance. / (idiomatic) Under suspicion; subject to critical inspection.

Already done; within one's experience; practiced.

(Australia, New Zealand) Under pressure to perform, e.g. at work or in a sports contest. / Used other than figuratively or idiomatically: see under, pump.

(idiomatic) Under great pressure to perform. / (poker) Of, pertaining to, or in the situation of first player to act on the first round of betting.

(transitive) To drink more alcohol than (someone) while remaining relatively sober.

Operating a motor vehicle while impaired due to the consumption of drugs or alcohol.

(idiomatic, of a person) Angry, agitated. / (idiomatic, colloquial, slang, of a person) Sexually aroused.

The small trees and other plants that clutter the floor of a forest.

(transitive) To clear (an area) of underbrush. / (intransitive) To work among the underbrush.