Undulate, a.
Etymology: [L. undulatus undulated, wavy, a dim. from unda a wave; cf. AS. unnr; perhaps akin to E. water. Cf. Abound, Inundate, Redound, Surround.]
Same as Undulated.
2 other Webster entries under this spelling
Undulate, v. t. [imp. & p. p. Undulated; p. pr. & vb. n. Undulating.]
To cause to move backward and forward, or up and down, in undulations or waves; to cause to vibrate. Breath vocalized, that is, vibrated and undulated. Holder.
Undulate, v. i.
To move in, or have, undulations or waves; to vibrate; to wave; as, undulating air.
Shades of meaning
Fernald has no entry of its own for undulate; he lists it under fluctuate.
Where he writes about it:
A pendulum oscillates; waves fluctuate or undulate; a light or a flame wavers; a frightened steed swerves from his course; a tool or weapon swerves from the mark or line; the temperature varies; the wind veers when it suddenly changes its direction. — from fluctuate