Douglas Harper's Etymology Dictionary
Wiktionary
a. Pertaining to only one direction, e.g.: where all component parts are aligned in the same direction in space.
WordNet
adj. operating or moving or allowing movement in one direction only; "a unidirectional flow"; "a unidirectional antenna"; "a unidirectional approach to a problem" [ant: bidirectional]
Usage examples of "unidirectional".
Cyfer will appreciate the implications: a colinear, unidirectional, non-overlapping, redundant triplet code.
Flake tools with unifacial, unidirectional chipping, like those found at Calico, are typical of the European eoliths.
The very metaphysical presuppositions differ: space does not conform to Euclidean geometry, time does not form a continuous unidirectional flow, causation does not conform to Aristotelian logic, man is not differentiated from non-man or life from death, as in our world.