|a fool or simpleton; ninny.|
|a chattering or flighty, light-headed person.|
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
Learn more about weir with a free trial on Britannica.com.