alveus
/ˈalvɪəs/noun
The bed or channel of a river; specifically that followed by the river flowing in its natural or ordinary course. Now usually in legal contexts.
Origin
Late 17th century (in an earlier sense). From classical Latin alveus hollow trough-shaped vessel, trough, bath tub, hull, hold, ship, boat, channel or bed (of a river or trench), beehive, probably related to alvus belly.