"to turn away in speaking or writing from the direct or appointed course," 1520s, from Latin digressus, past participle of digredi "to go aside, depart, deviate," from dis- "apart, aside" (see dis-) + gradi "to step, go" (from PIE root *ghredh- "to walk, go"). Or perhaps it is a back-formation from digression. Related: Digressed; digressing.
