ten (n., adj.) Look up ten at Dictionary.com
Old English ten (Mercian), tien (West Saxon), adjective and noun, from Proto-Germanic *tehun (cognates: Old Saxon tehan, Old Norse tiu, Danish ti, Old Frisian tian, Old Dutch ten, Dutch tien, Old High German zehan, German zehn, Gothic taihun "ten").

The Germanic words are from PIE *dekm "ten" (cognates: Sanskrit dasa, Avestan dasa, Armenian tasn, Greek deka, Latin decem (source of Spanish diez, French dix), Old Church Slavonic deseti, Lithuanian desimt, Old Irish deich, Breton dek, Welsh deg, Albanian djetu "ten").

Meaning "ten o'clock" is from 1712. Tenner "ten-pound note" is slang first recorded 1861; as "ten-dollar bill," 1887 (ten-spot in this sense dates from 1848). The Texan's exaggerated ten-gallon hat is from 1919. The ten-foot pole that you wouldn't touch something with (1909) was originally a 40-foot pole; the notion is of keeping one's distance, the same as in the advice to use a long spoon when you dine with the devil. Ten-four "I understand, message received," is attested in popular jargon from 1962, from use in CB and police radio 10-code (in use in U.S. by 1950).