Definition of "undulation" []

• A regular rising and falling or movement to alternating sides; movement in waves. (noun)
• A wavelike form, outline, or appearance. (noun)
• One of a series of waves or wavelike segments. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "There are two motions of the waves -- one up and down, which we call undulation, the other to and fro, which we call fluctuation."
• "The undulation is the work of two collaborators: it expresses both the nature of the object which provokes it and that of the nervous apparatus which is its vehicle."
• "The poor, I found, believed that this pious exercise dispersed the evil spirits of the storm; while the better sort conceived that it occasioned some kind of undulation in the air, and so broke the continuity of the electric fluid."