"to beat or pulse rapidly, to throb," 1620s, from Latin palpitatus, past participle of palpitare "to throb, flutter" (see palpable). Related: Palpitated; palpitating.

Middle English quaken, from Old English cwacian "quake (of the earth), tremble, shudder (of persons, from cold, emotion, fear, fever, etc.), chatter (of teeth)," related to cweccan "to shake, swing, move, vibrate," words of unknown origin with no certain cognates outside English. Perhaps somehow imitative (compare quag, quaver, quiver (v.), Middle English quaven "tremble, shake, palpitate," c. 1200). Related: Quaked; quaking. In Middle English formerly also with strong past-participle form quoke. The North American quaking aspen is so called by 1822.