n. & v.
n. 1 something done; a deed; an action. 2 the process of doing something (caught in the act). 3 a a piece of entertainment, usu. one of a series in a programme. b the performer(s) of this. 4 a pretence; behaviour intended to deceive or impress (it was all an act). 5 a main division of a play or opera. 6 a a written ordinance of a parliament or other legislative body. b a document attesting a legal transaction. 7 (often in pl.) the recorded decisions or proceedings of a committee, an academic body, etc. 8 (Acts) ( in full Acts of the Apostles) the New Testament book relating the growth of the early Church.
v. 1 intr. behave (see how they act under stress). 2 intr. perform actions or functions; operate effectively; take action (act as referee; the brakes failed to act; we must act quickly). 3 intr. (also foll. by on) exert energy or influence (the medicine soon began to act; alcohol acts on the brain). 4 intr. a perform a part in a play, film, etc. b pretend. 5 tr. a perform the part of (acted Othello; acts the fool). b perform (a play etc.). c portray (an incident) by actions. d feign (we acted indifference). act for be the (esp. legal) representative of. act of God the operation of uncontrollable natural forces. act of grace a privilege or concession that cannot be claimed as a right. act on (or upon) perform or carry out; put into operation (acted on my advice). act out 1 translate (ideas etc.) into action. 2 Psychol. represent (one's subconscious desires etc.) in action. act up colloq. misbehave; give trouble (my car is acting up again). get one's act together sl. become properly organized; make preparations for an undertaking etc. get into the act sl. become a participant (esp. for profit). put on an act colloq. carry out a pretence. actable adj. (in sense 5 of v.). actability n. (in sense 5 of v.).
[ ME ult. f. L agere act- do ]