In As You Like It,
Rosalind has gone "undercover" as a young man named Ganymede. The shepherdess Phebe has fallen for Ganymede big-time, much to the chagrin of Silvius, who is in love with Phebe. (Love triangles involving cross-dressing characters are pretty common in Shakespeare's comedies.)
In Act IV, Scene 3, Silvius delivers a letter to Rosalind (still disguised as Ganymede) written by Phebe. Rosalind accuses the illiterate Silvius of writing the letter himself, saying that it is a harsh and cruel letter, too horrible for a woman to have written:
Why, 'tis a boisterous and a cruel style;
A style for challengers: why, she defies me,
Like Turk to Christian: women's gentle brain
Could not drop forth such giant-rude invention,
Such Ethiop words, blacker in their effect
Than in their countenance.
In the phrase "Ethiop words," Ethiop refers to Ethiopia, a country in eastern Africa. If you look at the larger phrase, you'll find that Shakespeare has personified the words in the letter. "Such Ethiop words, blacker in their effect than in their countenance." Countenance is another word for face, and the face of one of the dark-skinned natives of Ethiopia is black.
In Western culture, the color black has long been a symbol for evil, mystery, fear, and death, and that's the symbol Shakespeare uses here. "Ethiop words" are "black words," words of cruelty. Is this phrase racist? Most likely, by today's standards. Shakespeare's audiences, though, would not have given the underlying ethics of the phrase a second thought.
Later in this scene, we learn that Rosalind is only teasing Silvius. She goes on to read the letter aloud, and even he can understand that it's really a love letter from Phebe.