What is the origin of undulate?
Something that undulates, as a flag or rhythm, moves side to side or rises and falls like a wave. Indeed, its origin is Latin unda “wave,” via undulātus “waved, wavy,” composed of –ula, a diminutive suffix, and –ātus, a past participle suffix. Unda also yields English abound, abundant, inundate, redound, redundant, and surround. Latin unda in turn comes from the Proto-Indo-European root wed– “water, wet,” ultimate source of the names of two substances that may cause some to undulate, as it were, on their feet: vodka (via Russian) and whiskey (Irish or Scots Gaelic). Best to stay hydrated, another derivative of wed-, via Greek hýdōr “water.” Undulate entered English in the 1600s.