tellus.

Uncertain, but the most likely cognates include Old Irish talam (“earth”) (reflecting Proto-Celtic *talamū, perhaps earlier *telamū), Lithuanian tilės (“flooring, bottom of a barge”), pã-talas (“bed”), Old Prussian talus (“floor”), Old Church Slavonic тъла pl (tŭla, “foundation, bottom”), Proto-Germanic *þelą (“floor; floorboard, type of plank”), and Sanskrit तल (tala, “surface, palm/sole, bottom, floor”). All are possibly derived from Proto-Indo-European *telh₂- (“ground, floor”), a special use of the verbal root *telh₂- (“to bear, carry, lift, support”). The term is unique in Latin in being the only polysyllabic s-stem with a long ū-vowel in the suffix. Also of interest is the ablaut between e in tellūs and *o in medi-tullium (“inner land”). De Vaan suggests, among other possibilities, that the term may derive from an original *-u-stem (but with o-grade ablaut somewhere in the paradigm, which is not usually reconstructed for this type) that was later extended with an s-suffix. He posits a Proto-Italic pre-form *teln- containing a suffixal element *-n-, but for formal reasons the affixation must post-date the loss of the PIE laryngeal in *telh₂-; it may have arisen by analogy with tollō (“to lift”) (Proto-Italic *tolnō). Compare the on-stem of Proto-Germanic *þiljǭ (“board, plank, floorboard; flooring, deck”) and the mon-stem of both Celtic and Ancient Greek τελαμών (telamṓn, “strap”, literally “that which supports”).