late 14c., directen, "to write or address (a letter, words)" to someone, also "to point or make known a course to," from Latin directus past participle of dirigere "set straight, arrange; give a particular direction to, send in a straight line; guide" a thing, either to something or according to something, from dis- "apart" (see dis-) + regere "to direct, to guide, keep straight" (from PIE root *reg- "move in a straight line"). Compare dress; address.
Sense of "to point or aim in a straight line toward a place or an object" is from c. 1400. Meaning "to govern, regulate as to behavior, prescribe the course or actions of" is from early 15c. Sense of "to order, ordain" is from 1650s. Sense of "to write the destination on the outside of a letter" had emerged by 17c. In reference to plays, films, etc., "to supervise and control the making of," it is attested from 1913. Related: Directed; directing.
c. 1400, "straight, undeviating, not crooked," from Old French direct (13c.) and directly from Latin directus "straight," adjectival use of past participle of dirigere "to set straight," from dis- "apart" (see dis-) + regere "to direct, to guide, keep straight" (from PIE root *reg- "move in a straight line"). Meaning "plain, expressive, not ambiguous" is from 1580s.