(chemistry, of a crystal or compound) Exhibiting optical activity.

(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

(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.

(chemistry) activated carbon

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

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

(volcanology, geology) A volcano that has erupted in the last 10,000 years, although not necessarily venting lava or gases now.

(chemistry, physics) The energy required to initiate a reaction. For example, the flame from the fuse of a firecracker provides a small initial amount of energy, after which the explosive reaction proceeds by itself, releasing a considerably larger quantity of energy. A small push given to a stable but top-heavy object may cause it to fall over; the potential energy released during the fall was present in the system all along but could not be realized as long as the object was upright and balanced.