1. (n.) The space enclosed 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.

2. (n.) 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.

3. (n.) The depression formed by the meeting of two slopes on a flat roof.

abysm abyss arroyo bottom bottom glade bottoms box canyon breach break canyon cavity chap chasm check chimney chink cirque cleft cleuch clough col comb combe corrie coulee couloir crack cranny crevasse crevice cut cwm dale defile dell dike dingle ditch donga draw excavation fault fissure flaw flume fracture furrow gap gape gash gill glen gorge groove grove gulch gulf gully hole hollow incision intervale joint kloof leak lunar rill moat notch nullah opening pass passage ravine rent rift rime rupture scissure seam slit slot split strath trench trough vale void wadi