adj. Consisting of or marked by only one part or element.adj. Of or relating to a telecommunications system in which only one message can be sent in either direction at one time.n. Mathematics A Euclidean geometric spatial element having the minimum number of boundary points, such as a line segment in one-dimensional space, a triangle in two-dimensional space, or a tetrahedron in three-dimensional space.n. Linguistics A word that has no affixes and is not part of a compound; a simple word.