Etymology means basically studying how a word has evolved historically. So I think the answer will be DERIVATION.
Sir Toby Belch is Olivia's drunken uncle, so he is not her suitor.
Antonio is a sea captain, and he is nobody's suitor.
Cesario is the person whom Orsino sends to woo Olivia for him, but falls in love with Viola.
So the correct answer, and Olivia's suitor is Sir Andrew Auguecheek.
