Source : Webster's Revised Unabridged Dictionary (1913)

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.