The article deals with the origin of the title of the Slavonic-Russian Book of Kaaf which has been still attributed to a hazy Hebrew source. In fact, the name of the second son of Levi, Kohath (קהת), appeared in the title absolutely accidentally, and the title came from from the Greek gloss Καὰθ ἐκκλησιαστής included in the explanatory onomasticons of Biblical names. This gloss is, perhaps, connected with the corresponding passage in the Testament of Levi from the apocryphal Testaments of the Twelve Patriarchs. Moreover, the article contains comparative data of the spelling of Kohath’s name in Church Slavonic translations of the Pentateuch and in the Palaea Interpretata, in the latter not only in the Testament of Levi, but also in its main text. The adventures of the word Кааѳъ / Каафъ in medieval Russian writing turn out to be entirely literary, and not connected with any hypothetical verbal tradition, which might have proved to have been a tempting explanation for this word.