"The Taming of the Shrew" by William Shakespeare, Act II

The verb usually means "feel pain or be in pain." Katherina suffers because her father (and everyone else) thinks she is insufferable ("extremely unpleasant or annoying"). This is mostly her fault because she makes other people suffer with her violent hands and sharp tongue. But it is also partly because she has a strong spirit that conflicts with expectations of her as a gentlewoman (no mention is made of a mother who could've given her some tips).

To Hortensio, the disguised teacher, a fret is a "bar of metal across the fingerboard of a musical instrument." But Katherina puns on the word to focus on its connection to anger--an emotion that Hortensio stirred up when, after telling her she was playing the lute wrong, he tried to correct her fingering by bending her hand.

The Old French verb "desconfire" means "to defeat, destroy." In trying to teach Katherina, Hortensio gets a headful of lute and a mouthful of insults, which discomfit him. In hearing about this conflict, Petruchio says, "Now, by the world, it is a lusty wench; I love her ten times more than e'er I did. O, how I long to have some chat with her!" In contrast with other men who want a wife who is mild by nature, Petruchio prefers a spirited woman with whom he can prove his superiority and strength.

As the structure of the lines shows, railing is the opposite of sweet singing. It also contrasts with some of the words used in Petruchio's next example of how he will deal with Katherina. Someone who can rail is not mute ("unable to speak"); she could be voluble ("marked by a ready flow of speech"), but she is not using eloquence ("powerful and effective language").

The verb also means "disturb, especially by minor irritations" or "feel extreme anger." Because Petruchio is holding Katherina at the moment, her words are meant as a physical threat. But she also knows her reputation, so this could be interpreted as a warning tinged with self-pity. Despite being seen as too difficult to woo and marry, Katherina does not want to be an old maid. Yet, she has too much pride to fall into a seeming madman's arms.