Noah Webster
Undulation
UNDULA'TION, noun [from undulate.]
1. A waving motion or vibration; as the undulations of a fluid, of water or air; the undulations of sound. The undulations of a fluid are propagated in concentric circles.
2. In medicine, a particular uneasy sensation of an undulatory motion in the heart.
3. In music, a rattling or jarring of sounds, as when discordant notes are sounded together. It is called also beat.
4. In surgery, a certain motion of the matter of an abscess when pressed, which indicates its maturity or fitness for opening.