thousandyoudaoicibaDictYouDict[thousand 词源字典]
thousand: [OE] Thousand is a compound noun of some antiquity, which seems to mean etymologically ‘several hundreds’. Its first element probably comes from a base denoting ‘increase’ or ‘multiplicity’, which also produced Latin tumēre ‘swell’ (source of English tumour) and Sanskrit tuvi ‘much’; its second element is the same as the first element of English hundred. The combination resulted in a prehistoric Germanic *thusundi, which evolved into German tausend, Dutch duizend, Swedish tusen, Danish tusind, and English thousand. It is shared by the Slavic languages – Russian, for instance, has tysjacha.
=> hundred, thigh, thumb, tumour[thousand etymology, thousand origin, 英语词源]
thousand (adj.)youdaoicibaDictYouDict
Old English þusend, from Proto-Germanic *thusundi (cognates: Old Frisian thusend, Dutch duizend, Old High German dusunt, German tausend, Old Norse þusund, Gothic þusundi).

Related to words in Balto-Slavic (Lithuanian tukstantis, Old Church Slavonic tysashta, Polish tysiąc, Russian tysiacha, Czech tisic), and probably ultimately a compound with indefinite meaning "great multitude, several hundred," literally "swollen-hundred," with first element from PIE root *teue- (2) "to swell" (see thigh).

Used to translate Greek khilias, Latin mille, hence the refinement into the precise modern meaning. There was no general Indo-European word for "thousand." Slang shortening thou first recorded 1867. Thousand island dressing (1916) presumably is named for the region of New York on the St. Lawrence River.