The most common and most likely answer to this crossword clue is the 8 letter word UNDULATE
I've seen this crossword clue in The Daily Telegraph
U
N
D
U
L
A
T
E
Buddy explains!

The straight part
We know that "Wave" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case wave = undulate.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does UNDULATE mean?
UNDULATE verb- To cause to move in a wavelike motion.
- To cause to resemble a wave
- To move in wavelike motions.
- To appear wavelike.
- Wavy in appearance or form.
- Changing the pitch and volume of one's voice.
- (of a margin) sinuous, winding up and down.