- Having a wavy border or form. Also, rising and falling like a wave. For example, the border of a wound may be undulant, as may the edge of a rash. And sound waves may also be undulant. The word "undulant" comes from the Latin "undula" which is the diminutive of "unda" meaning wave. So "undula" is a little wave. Undulant fever, also called brucellosis, is an infectious disease characterized by a rising and falling (undulant) fever. It is caused by a bacterium called Brucella that can be transmitted in unpasteurized milk or cheese of cattle, sheep, and goats or by contact with diseased animals.
Medical dictionary. 2011.