n. [ F. terrain, from L. terra earth. ] 1. (Geol.) A group of rocks having a common age or origin; -- nearly equivalent to formation, but used somewhat less comprehensively. [ 1913 Webster ]

n. (Geog.) 2. A region or limited area considered with reference to some special feature; as, the terrane of a river, that is, its drainage basin. [ Webster 1913 Suppl. ]