adj., adv., & n.
adj. additional; more than is usual or necessary or expected.
adv. 1 more than usually. 2 additionally (was charged extra).
n. 1 an extra thing. 2 a thing for which an extra charge is made. 3 a person engaged temporarily to fill out a scene in a film or play, esp. as one of a crowd. 4 a special issue of a newspaper etc. 5 Cricket a run scored other than from a hit with the bat. extra cover Cricket 1 a fielding position on a line between cover-point and mid-off, but beyond these. 2 a fielder at this position. extra size outsize. extra time Sport a further period of play at the end of a match when the scores are equal.
[ prob. a shortening of EXTRAORDINARY ]