'Terrestrial' is Latin for 'of the earth' — from 'terra.' Land-dwelling, or relating to our planet.
Of, on, or relating to the earth. Living on or in the ground (as opposed to aquatic, arboreal, or aerial). Of or relating to the earth as opposed to other celestial bodies.
From Latin 'terrestris' (of or belonging to the earth, earthly, on land), from 'terra' (earth, ground, dry land, a land), from PIE *ters- (to dry up, to become dry). The root *ters- conveys the essential quality of land as something dry, in contrast to the sea. It produced Latin 'torrēre' (to parch, to roast), English 'torrid' and 'toast,' and also 'terrace,' 'terrain,' 'territory,' and 'Mediterranean
The word 'extraterrestrial' — from Latin 'extra' (outside) + 'terrestris' (of the earth) — literally means 'from outside the earth.' When astronomers speak of 'terrestrial planets,' they mean rocky planets like Earth, Mars, Venus, and Mercury, as opposed to the gas giants. The irony is that 'terrestrial' (earthy, of the ground) is now used to describe planets that are nothing