word-forming element meaning "outside; beyond the scope of; in addition to what is usual or expected," in classical Latin recorded only in extraordinarius, but more used in Medieval Latin and modern formations; it represents Latin extra (adv.) "on the outside, without, except," the old fem. ablative singular of exterus "outward, outside," comparative of ex "out of" (see ex-).
late 14c., "of or pertaining to the earth," with + -al (1) + from Latin terrestris "earthly, of the earth, on land," from terra "earth" (from PIE root *ters- "to dry"). Originally opposed to celestial; natural history sense of "living on land" is attested from 1630s. The noun meaning "a human being, a mortal" is recorded from 1590s.
<a href="https://www.etymonline.com/word/extraterrestrial">Etymology of extraterrestrial by etymonline</a>
Harper, D. (n.d.). Etymology of extraterrestrial. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/extraterrestrial