acting (adj.) Look up acting at Dictionary.com
1590s, "putting forth activity," present participle adjective from act (v.). Meaning "performing temporary duties" is from 1797.
acting (n.) Look up acting at Dictionary.com
c.1600, "performance of deeds;" 1660s, "performance of plays;" verbal noun from present participle of act (v.). Acting out in psychology is from 1945.