I would guess that this word is derived from waste (english) + weir (german)? Can anyone provide a more definitive derivation explanation? (couldn't find anything via etymonline.com) Will keep googling for more info and update if I find anything interesting.
I just had to split up the terms and search for them individually:
c.1200, "desolate regions," from O.Fr. wast, from L. vastum, neut. of vastus "waste" (see waste (v.)); replacing O.E. westen, woesten "a desert, wilderness," from the Latin word. Meaning "useless expenditure" is recorded from c.1300; sense of "refuse matter" is attested from early 15c. Waste basket first recorded 1850. Waste-paper first recorded 1580s.
O.E. wer "dam, fence, enclosure," especially one for catching fish (related to werian "dam up"), from P.Gmc. *warjanan (cf. O.N. ver, O.Fris., M.Du. were, Du. weer, O.H.G. wari, Ger. Wehr "defense, protection," Goth. warjan "to defend, protect"), from PIE *wer- "to cover, shut" (cf. Skt. vatah "enclosure," vrnoti "covers, wraps, shuts;" Lith. uzveriu "to shut, to close;" O.Pers. *pari-varaka "protective;" L. (op)erire "to cover;" O.C.S. vora "sealed, closed," vreti "shut;" O.Ir. feronn "field," prop. "enclosed land")
So you were right Jamie, weir is primarily from Old English, but as you can see from the lengthy etymology, it also may have been derived from proto-Germanic, Latin, Sanskrit, Old Persian and number of other languages.