the world > space > relative position > closed or shut condition > that which or one who closes or shuts > a barrier > [noun] > in a river (8)
A grating or frame of parallel bars in a river to obstruct the passage of fish, or other solid bodies, without obstructing the flow of the water…
A floating barrier (see quot. 1777).
Any (physical or immaterial) barrier or obstruction; (U.S.) spec. (a) a stoppage or obstruction on a railway; (b) a barrier on a river.