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

(chemistry) Any of several similar radiochemical techniques of analysis in which a subatomic particle or gamma ray is captured by a nuclide to form a second stable nuclide which is then measured.

plural of activation analysis

The increase in rate of a chemical reaction caused by the presence of a catalyst. / An amount of catalyst, expressed as the increase of the rate of its reaction.

(organic chemistry) Any of a wide range of techniques, often using catalysts, in which a carbon to hydrogen covalent bond of an organic compound is made to cleave in order to replace the hydrogen with a functional group.

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.

plural of active couple

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

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

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