unidirectional

Pertaining to only one direction, e.g.: where all component parts are aligned in the same direction in space.

[...] a reversible booster was fitted to the trailing bogie; all previous applications on the L.N.E.R. for use in main line traffic had been of unidirectional boosters, […]

Equally important is the class mailing list, which facilitates two-way communication at a distance. (By contrast, the web page is basically a unidirectional teacher-to-student communication.)

Not subject to change or reversal of direction.

A fabric in which the majority of fibers run in the same single direction.