For decades, the Kitāb al-Talḫīṣ, a pharmacological dictionary composed by the Jewish biblical lexicographer and exegete Abū l-Walīd Marwān Ibn Ǧanāḥ (ca. 980–1040), was thought to be lost. Even its discovery in 1979 by Fuat Sezgin, who gave a brief outline of the text preserved in an Istanbul manuscript, went entirely unnoticed by the scholarly community until 2010, when Fabian Käs gave a preliminary account of the work in his masterful concordance of the minerals in Arabic pharmacognosy. During a recent study trip to the Süleymaniye Library in Istanbul, the present writer was able to examine at first hand the work preserved in MS Aya Sofia 3603. A physical description of the work and its purpose, as set out in Ibn Ǧanāḥ’s introduction, are presented, followed by a characterization of the author’s methodology. More than just a glossary, Ibn Ǧanāḥ’s Talḫīṣ, written in the adab style, draws on multiple medical, botanical and even literary and philosophical sources. Ibn Ǧanāḥ’s concept of an independent medical dictionary may have been inspired by his earlier composition of the Kitāb al-uṣūl, the Book of Roots, a bilingual biblical dictionary. Significant details of the classical Greek and Arab sources upon which Ibn Ǧanāḥ drew are discussed, along with his relation to the Qayrawān school and his exchanges with his contemporaries in al-Andalus. Of particular interest is an Arabic quote from Isaac Israeli’s Book of Elements. A list of quotations in the works of later authorities is included in an attempt to gauge the work’s influence. In conclusion, the originality of this composition is highlighted, as well as the possibility of a specifically Jewish contribution to the discipline of pharmacognosy.