digression (n.)

late 14c., digressioun, "act of deviating from the main subject matter in speaking or writing," from Latin digressionem (nominative digressio) "a going away, departing," noun of action from past participle stem of digredi "to deviate," from dis- "apart, aside" (see dis-) + gradi "to step, go" (from PIE root *ghredh- "to walk, go").