Saying softly, indirectly, or in disguise something harsh, ugly, or forbidden to name.
In Dom Casmurro
Even so, I found the courage to pour the substance into the cup
The "substance" takes the place of "poison": the narrator avoids naming what he pours into the cup, and the disguise of the word softens the gesture without hiding what it is.
Chapters CXXXVI to CXLVIII: The Cup, the Separation, and the Rest, the narrator