Old English toð (plural teð), from Proto-Germanic *tanth, *tunth (cf. Old Saxon, Danish, Swedish, Dutch tand, Old Norse tönn, Old Frisian toth, Old High German zand, German Zahn, Gothic tunþus), from PIE *dont-/*dent- "tooth" (cf. Sanskrit danta, Greek odontos, Latin dens, Lithuanian dantis, Old Irish det, Welsh dent). Plural form teeth is an instance of i-mutation. Application to tooth-like parts of other objects (saws, combs, etc.) first recorded 1520s.
n. pl. teeth (tēth)
One of a set of hard, bonelike structures rooted in sockets in the jaws of vertebrates, typically composed of a core of soft pulp surrounded by a layer of hard dentin that is coated with cement or enamel at the crown and used chiefly for biting or chewing food or as a means of attack or defense.
Plural teeth (tēth)
A hard structure, embedded in the jaws of the mouth, that functions in chewing. The tooth consists of a crown, covered with hard white enamel; a root, which anchors the tooth to the jawbone; and a “neck” between the crown and the root, covered by the gum. Most of the tooth is made up of dentin, which is located directly below the enamel. The soft interior of the tooth, the pulp, contains nerves and blood vessels. Humans have molars for grinding food, incisors for cutting, and canines and bicuspids for tearing.
Aged; advanced in age: The actor is a bit long in the tooth to be playing Tom Sawyer
[1852+; fr the practice of judging the age of horses by the length of teeth]