Basin, Or Bason (the older form bacin is found in many of the Romanic languages, from the Late Lat. baccinus or bacchinus, probably derived from bacca, a bowl), a round vessel for holding liquids. Hence the term has various technical uses, as of a dock constructed with flood-gates in a tidal-river, or of a widening in a canal for unloading barges; also, in physical geography, of the drainage area of a river and its tributaries.

In geology, "basin" is equivalent to a broad shallow syncline, i.e. it is a structure proper to the bed rock of the district covered by the term; it must not be confused with the physiographic river basin, although it occasionally happens that the two coincide to some extent. Some of the better known geological basins in England are, the London basin, a shallow trough or syncline of Tertiary, Cretaceous and Jurassic rocks; the Hampshire basin, of similar formations; and the numerous coal basins, e.g. the S. Wales coalfield, the Forest of Dean, N. Staffordshire coalfield, etc. The Paris basin is made of strata similar to those in the London and Hampshire basins. Strictly speaking, a structural basin is formed of rock beds which exhibit a centroclinal dip; an elongated narrow syncline or trough is not a basin. "Rock-basins" are comparatively small, steep-sided depressions that have been scooped out of the solid rock in mountainous regions, mainly through the agency of glaciers (see Cirque). Lakes sometimes occupy basins that have been caused by the removal in solution of some of the more soluble constituents (rock salt, etc.) in the underlying strata; occasionally lake basins have been formed directly by crustal movements.