oscillation (n.)
1650s, from French oscillation, from Latin oscillationem (nominative oscillatio), noun of action from past participle stem of oscillare "to swing," supposed to be from oscillum "little face," literally "little mouth," a mask of open-mouthed Bacchus hung up in vineyards as a charm (the sense evolution would be via the notion of "swing in the breeze"); from PIE *os- "mouth" (see oral).