a long depression in the surface of the land that usually contains a river
The space inclosed between ranges of hills or mountains; the strip of land at the bottom of the depressions intersecting a country, including usually the bed of a stream, with frequently broad alluvial plains on one or both sides of the stream. also used figuratively.
The place of meeting of two slopes of a roof, which have their plates running in different directions, and form on the plan a reentrant angle.
The depression formed by the meeting of two slopes on a flat roof.