Movement ahead or forward. / (nautical) Forward motion, or its rate.

Used other than figuratively or idiomatically: see off, top, head. / (idiomatic) In an extemporaneous manner; without careful thought, preparation, or investigation.

The science and practice of community hygiene; includes preventive medicine, health education, sanitation and environmental safety.

Determined to do as one pleases, and not as others want.

(chiefly UK) A male school principal.

The hub of a propeller / The central part of a propeller, into which the blades fit

(idiomatic) To progress; to move forward.

(electronics) The ability of an amplifier to handle strong signals (or loud sounds) free from distortion.

(idiomatic) To act in a haphazard or aimless way; to act frantically or without control.

The vertical clearance above someone's head, as in a tunnel, doorway etc. / The vertical measurement, top to bottom, for example for clearance under a bridge.