a small dam in a river or stream.
a fence, as of brush or narrow boards, or a net set in a stream, channel, etc., for catching fish.

before 900; Middle English were, Old English wer, derivative of root of werian to defend, dam up Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
weir (wɪə)
1.  a low dam that is built across a river to raise the water level, divert the water, or control its flow
2.  a series of traps or enclosures placed in a stream to catch fish
[Old English wer; related to Old Norse ver, Old Frisian were, German Wehr]

Weir (wɪə)
1.  Judith. born 1954, Scottish composer, noted esp for her opera A Night at the Chinese Opera (1987)
2.  Peter. born 1944, Australian film director; his films include Dead Poets Society (1989), The Truman Show (1998), and Master and Commander (2003)

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

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").
Online Etymology Dictionary, © 2010 Douglas Harper
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Encyclopedia Britannica


any control or barrier placed in an open channel to permit measurement of water discharge. The latter may be computed from a formula expressing the discharge in terms of crest length of the weir, depth of flow above the weir, weir geometry, and other factors. A variety of weirs have been used in streams, the so-called sharp-crested and trapezoidal forms being relatively common; but broad-crested, triangular, and contracted weirs are also favoured in certain circumstances. Spillways, controls, and embankments designed to permit discharge measurements are simply different kinds of broad-crested weirs

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
To blame the weir for environmental destruction which has already occurred is
  political humbug.
Spawning fish were transferred upstream of the weir, while sea lampreys were
Enhanced oil spill recovery rate using the weir skimmer.
Weir sticks are commercially calibrated stick or staff gage type devices which
  may be placed by hand upon the crest of a weir.
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