"pertaining to the earth," 1846, from -ian + Latin tellus (genitive telluris) "earth, land, ground; the earth" (related to Tellus, Roman goddess of the earth), probably from PIE root *telho- "ground, floor" (source also of Sanskrit talam "plain, sole of the foot;" Greek telia "dice board;" Latvian telint "to spread out;" Lithuanian tils "bottom of a barge, flooring," patalas "bed;" Old Prussian tallus "floor;" Old Church Slavonic tilo "floor;" Russian potolok "ceiling;" Old Irish talam "earth;" Old Norse ilja, Middle Dutch dele "plank"). Or possibly from PIE *telh- "to bear." As a noun, "inhabitant of Earth" (with reference to supposed inhabitants of other worlds) from 1847.
Figurative sense "climax, culmination" is from 1640s. A term from Ptolemaic astronomy, which regarded the earth as the center of the universe and applied the word to the sun and planets; for these bodies it was displaced in the Copernican system by aphelion. Adjective forms are apogeal, apogean, apogeic.
early 14c., also gemetrie, gemetry, from Old French geometrie (12c., Modern French géométrie), from Latin geometria, from Greek geometria "measurement of earth or land; geometry," from combining form of gē "earth, land" (see Gaia) + -metria "a measuring of" (see -metry). Old English used eorðcræft "earth-craft" as a loan-translation of Latin geometria.