gap-toothed adj.

early 14c., "an opening in a wall or hedge; a break, a breach," mid-13c. in place names, from Old Norse gap "chasm, empty space," related to gapa "to gape, open the mouth wide," common Proto-Germanic (cognates: Middle Dutch, Dutch gapen, German gaffen "to gape, stare," Swedish gapa, Danish gabe), from PIE root *ghieh- "to yawn, gape, be wide open."

From late 14c. as "a break or opening between mountains;" broader sense "unfilled space or interval, any hiatus or interruption" is from c. 1600. In U.S., common in place names in reference to a deep break or pass in a long mountain chain (especially one that water flows through), a feature in the middle Appalachians.

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.

"opening, entrance," Old English geat (plural geatu) "gate, door, opening, passage, hinged framework barrier," from Proto-Germanic *gatan (source also of Old Norse gat "opening, passage," Old Saxon gat "eye of a needle, hole," Old Frisian gat "hole, opening," Dutch gat "gap, hole, breach," German Gasse "street, lane, alley"), of unknown origin. Meaning "money collected from selling tickets" dates from 1896 (short for gate money, 1820). Gate-crasher is from 1926 as "uninvited party guest;" 1925 in reference to motorists who run railway gates. Finnish katu, Lettish gatua "street" are Germanic loan-words.