dent-

Root for tooth, yielding Latin dens/dentis, Greek odous/odontos, Sanskrit dant-.‌​‌​‍​‌​‍​‍​‌​‌​‍​‍​‌​‌​‌​‍​‍​‌​‌​‍​‌​‌​‌​‌​‌​‌​‍​‌​‍​‌​‌​‍​‌​‍

Discussion

The PIE noun *dent- (tooth, fang — genitive *dn̥tós) is a participial formation from the verbal root‌​‌​‍​‌​‍​‍​‌​‌​‍​‍​‌​‌​‌​‍​‍​‌​‌​‍​‌​‌​‌​‌​‌​‌​‍​‌​‍​‌​‌​‍​‌​‍ *h₁ed- (to eat, to bite), literally meaning "the biting one" — the tooth defined by its function rather than its position. The word belongs to the PIE body-part vocabulary, a stratum of the lexicon so conservatively inherited that the same word for tooth has been in continuous use across the IE family for at least five thousand years.

Latin dēns (tooth — genitive dentis) continues the form with minimal change and generated the English dental vocabulary: dental (pertaining to teeth), dentist (a tooth-specialist), denture (a set of artificial teeth), indent (to make tooth-like notches — a legal document was originally "indented" by tearing a zigzag edge so the two halves could be matched), and trident (tri-dēns, "three-toothed" — Poseidon's three-pronged weapon). The word dandelion descends from French dent-de-lion ("lion's tooth," from the jagged shape of the leaves).

Greek odoús (ὀδούς, genitive odóntos, "tooth") preserves the root with a prothetic vowel characteristic of Greek, giving English: orthodontics ("straight-tooth" treatment), periodontal (around the teeth), and the suffix -odon/-odont used in taxonomic naming (mastodon, "breast-tooth" — named for the nipple-shaped projections on its molars).

English tooth itself descends from Old English tōþ, from PGmc *tanþuz, from PIE *dent- with regular Grimm's Law shifts: *d > *t, *t > *þ. German Zahn shows the expected High German consonant shift. The word's form is so ancient and so regularly inherited that the correspondence tooth/dēns/odoús/dánta (Sanskrit) is one of the first examples taught in introductory Indo-European linguistics.

Sanskrit dánta- (tooth) and the related Avestan danta- confirm the Indo-Iranian reflex. Lithuanian dantìs (tooth) preserves the Baltic form. Old Irish dét (tooth) provides the Celtic cognate.

The participial origin — tooth as "the eater" — reveals a conceptual world in which body parts were named for what they DO rather than where they are. This agentive naming pattern appears in other PIE body-part terms and suggests that the proto-speakers conceptualised the body as a collection of functional agents rather than a static anatomy.

Notes

Pokorny 289. Present participle of *h1ed- (to eat): the biting one.