Undulation (4)
'undulation' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for wave that I've seen before include "may have a crest at the top?" , "Shake a hand in the air" , "Undulating curve" , "Move hand to and fro as greeting" , "60s cinematic movement with 1a [NEW]" .)
'undulation' is the definition.
(I know that ripple is a type of oscillation)
This is the entire clue.
(Other definitions for ripple that I've seen before include "A small wave, or a gentle sound as of laughter" , "Slight surface wave" , "Small wave on a liquid's surface" , "undulation" , "Small wave or surface disturbance" .)