Lyrics? There are none, as that's purely instrumental. Onomatopoeia? Assuming it's a pure sine wave, probably just an "ooooooo" without any glottal plosive at the beginning. A pure sine wave wouldn't be a "woooo", that would be a sine wave with some kind of envelope filter or something at the beginning of it. It wouldn't be "ooooOOOOOooooo" unless there's an increase in amplitude in the middle or like, another additional sine wave of a slightly different frequency than the first and going in and out of phase with it or something along those lines. An "iiiiiiiiiii" sung in a head voice might be appropriate if the sine wave is really high in pitch.

{}

(empty set)

Depends on the frequency. Could be DOOOOOOOOOOOOOON, could be DUUUUUUUUUUUUUUN, could be DIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIN.

Roller coaster noises? WwooooOOOoooooo Siren? Not lyrics Anything that's a palindrome? Or at least short ones: radar https://en.wikipedia.org/wiki/Palindrome#Classical_music

Sequential or concurrent playback of the sinewaves?
Or even both?
Then lyrics could be anything you want, look up Fourier Transform.

Mongolian throat singing.

Tuva.

Boop (if you can make it go off and on)

Depending on its frequency it can be anything from a womp to a shrieking eeeeeee.