late 14c., direccioun, "action of directing or guiding," from Latin directionem (nominative directio) "a making straight, a straight line, a directing (toward something)," noun of action from past-participle stem of dirigere "to set straight, arrange; give a particular direction to," from dis- "apart" (see dis-) + regere "to direct, to guide, keep straight" (from PIE root *reg- "move in a straight line").
Meaning "the act of governing, administration" is from early 15c. Sense of "relative position without regard to distance" is from 1660s. Meaning "course pursued by a moving object" is from 1660s.
Sense of "order, instruction in how to proceed" is from early 15c.; specific sense of "instruction in how to get somewhere" is from 1590s (directions in this sense is by 1749). Related: Directional.
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Definitions of unidirectional
operating or moving or allowing movement in one direction only;