weir UK /wɪə̯/US /wɪɹ/noun 3verb 1forms 3 noun3 •An adjustable dam placed across a river to regulate the flow of water downstream.The weir must not represent a physical barrier to fish migration, both locally and throughout the whole river system. If necessary, a fishway is included in the weir. — 1997 •A fence placed across a river to catch fish.The Taff is naturally a good salmon river, the Ely a sea trout river, but what with weirs and pollusions the fish have been pretty well exterminated. — 1879 •(no longer used) Seaweed. verb1 •To put a weir, or weirs (in a river) formsweired · weiring · weirs
