acting (n.) Look up acting at
c. 1600, "performance of deeds;" 1660s, "performance of plays;" verbal noun from present participle of act (v.). Acting out "abnormal behavior caused by unconscious influences" is from 1945 in psychiatry.
acting (adj.) Look up acting at
1590s, "putting forth activity, active," present participle adjective from act (v.). Meaning "performing temporary duties" is from 1797.