simplex

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Consisting of or marked by only one part or element.
• adjective Of or relating to a telecommunications system in which only one message can be sent in either direction at one time.
• noun 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.
• noun Linguistics A word that has no affixes and is not part of a compound; a simple word.

from The Century Dictionary.

• Simple; single: applied to telegraphy.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Single, simple; not complex.
• adjective telecommunications unidirectional
• noun geometry, algebraic topology An analogue in any dimension of the triangle or tetrahedron: the convex hull of n+1 points in n-dimensional space.
• noun linguistics A simple word, one without affixes.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective having only one part or element
• adjective allowing communication in only one direction at a time, or in telegraphy allowing only one message over a line at a time