The Collaborative International Dictionary
Geosynclinal
Geosynclinal \Ge`o*syn*cli"nal\, n. [Gr. ge`a, gh^, the earth + E. synclinal.] (Geol.) the downward bend or subsidence of the earth's crust, which allows of the gradual accumulation of sediment, and hence forms the first step in the making of a mountain range; -- opposed to geanticlinal.
Wiktionary
geosynclinal
n. (context geology English) 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.