(set phrase) One who acts or reacts boldly, without hesitation, and often without forethought, especially in situations which are adventurous or dangerous.

plural of action verb

(metallurgy) an electrochemical action that generates electrical current between two metals of dissimilar electrode potential.

(law) countersuit

Abbreviation of nomen actionis.

(sociology) Research where the researcher themselves are an agent of social action.

(firearms, historical) An early form of breechloading firearm action, where the heavy breechblock tilted downwards across a bolt mounted in the rear of the breechblock, operated by a lever under the rifle.

(music) A pianoforte action, used in grand pianos, in which special devices are employed to obtain perfect action of the hammer in striking and leaving the string.

plural of zone of action

plural of actio popularis