Words related to us
Old English we, first person plural pronoun, "I and another or others," from Proto-Germanic *wejes (source also of Old Saxon wi, Old Norse ver, Danish vi, Old Frisian wi, Dutch wij, Old High German and German wir, Gothic weis "we"), from PIE *we- (source also of Sanskrit vayam, Old Persian vayam, Hittite wesh "we," Old Church Slavonic ve "we two," Lithuanian vedu "we two").
The "royal we" (use of plural pronoun to denote oneself) is at least as old as "Beowulf" (c.725); use by writers to establish an impersonal style is also from Old English; it was especially common 19c. in unsigned editorials, to suggest staff consensus, and was lampooned as such at least since 1853 (see wegotism).
pertaining to a proposed meta-family of languages including Indo-European, Semitic, Altaic, and Dravidian, 1966 (Nostratian is from 1931), from Latin nostratis "of our country," from nostras "our countrymen," plural of nostrum, neuter of noster "our," from nos "we" (from PIE *nes- (2); see us).
c. 1600, "a medicine made of secret ingredients by secret methods," but commonly "quack medicine," from Latin nostrum remedium "our remedy" (or some similar phrase), presumably indicating "prepared by the person offering it," from Latin nostrum, neuter of noster "our," from nos "we," from PIE *nes- (2); see us. In extended use, "a pet scheme for accomplishing something" (1749).
Old English toð (plural teð), from Proto-Germanic *tanthu- (source also of Old Saxon, Danish, Swedish, Dutch tand, Old Norse tönn, Old Frisian toth, Old High German zand, German Zahn, Gothic tunþus), from PIE root *dent- "tooth." Plural teeth is an instance of i-mutation.
The loss of -n- before spirants is regular in Old English, Old Frisian, and Old Saxon: compare goose (n.), five, mouth (n.). Also thought, from stem of think; couth from the stem of can (v.1); us from *uns.
Application to tooth-like parts of other objects (saws, combs, etc.) first recorded 1520s. Tooth and nail as weapons is from 1530s. The tooth-fairy is attested from 1964.