(geology) Of the Earth's crust, bending downward or subsiding and permitting the gradual accumulation of sediment.

(geology) The downward bend or subsidence of the Earth's crust, which permits the gradual accumulation of sediment and hence forms the first step in the formation of a mountain range.

plural of geosynclinal

(geology) A large, linear depression in the Earth's crust in which sediment accumulates.

plural of geosyncline