'simplex' definitions:
Definition of 'simplex'
(from WordNet)
adjective
Allowing communication in only one direction at a time, or in telegraphy allowing only one message over a line at a time; "simplex system"
adjective
Having only one part or element; "a simplex word has no affixes and is not part of a compound--like `boy' compared with `boyish' or `house' compared with `houseboat'"