(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.

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

plural of active couple

In set dances with more than one couple dancing, the couple doing the more complicated movement during any given portion of the dance. The role of active couple may pass from one couple to another. In many quadrilles, certain figures will have two active couples at any one time; in long set dances, quite often every other couple or every third couple is the active couple.

Partially active

Alternative spelling of pseudoactive

(biology) Movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.