In the article, the author applies Jadwiga Rafałowiczówna’s preserved correspondence to Elżbieta Sieniawska, focusing mainly on the varied lexical items related to diseases. The material gathered is compared with the lexicon of the 16th-century Polish language. Among the analysed terms there are one-word nouns of the Greek and Latin origin, as well as two-word names. What is also characteristic of the letters’ author is the use of euphemisms referring to death. When alluded to in such a manner, death became more tamed and natural a phenomenon.