Any activity done by an astronaut outside of a spacecraft etc; a spacewalk or moonwalk.

(physics) a property caused by asymmetrical molecular or crystal structure that enables a compound or crystal to rotate the plane of incident polarized light

capable of lowering the surface tension of a liquid

(grammar, uncountable) the form in which the subject of a verb carries out some action / (grammar, countable) a form in a particular language used to express the active voice

(astronomy) A galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy.

(physics, meteorology) The boundary between two different air masses, or a portion thereof, which produces appreciable cloudiness and precipitation and is usually accompanied by significant shifts in wind direction.

The specific compound in a natural or man-made mixture that is responsible for the mixture's activity.

Sewage that has been aerated and agitated in order to promote the growth of beneficial microorganisms that break down organic matter.

(chemistry) activated carbon

(chemistry) A very absorbent form of finely powdered carbon; used in purifying gases, and as an antidote for many poisons.