September is Etymology Month (6)

thousand O.E. þusend, from P.Gmc. *thusundi (cf. O.Fris. thusend, Du. duizend, O.H.G. dusunt, Ger. tausend, O.N. þusund, Goth. þusundi); related to words in Balto-Slavic (cf. Lith. tukstantis, O.C.S. tysashta, Pol. tysiąc, Czech tisic), and probably ultimately a compound with indefinite meaning "several hundred" or "a great multitude" (with first element perhaps related to Skt. tawas "strong, force"). Used to translate Gk. khilias, L. mille, hence the refinement into the precise modern meaning. There was no general IE word for "thousand." Slang shortening thou first recorded 1867. Thousand island dressing (1916) is presumably named for the region of New York on the St. Lawrence River.