The word cifir/cifr/cefr (الجفر) was used in the Islamicate World to describe a complex divinatory technique, which was based on the numerical values of the letters of the Arabic alphabet. This occult practice dates back to the early days of Islam and the Prophet’s cousin and son-in-law, Ali; it was him, who acted as its first practitioner and the one who allegedly composed the first book, which described the secrets that were hidden in the letters. Some of the most prominent scholars within the Lands of Islam such as Ibn Khaldun and Imam Ghazali spoke of the nature of cifr and the qualities of the people who were allowed to know and practice it. Throughout the course of centuries the practice found broad use, mainly within a political context, where it was used as a tool for the legalization of political authority through predictions of major future events of military, political and apocalyptic nature. This is, for example, the case in Miftah-ı Cifrü'l-Cami (Key to the comprehensive divination), a magnificently illustrated cifr treatise attributed to one of the most prolific lettrist masters, Şeyh Abdurrahman el-Bistami (d. 1454). Bistami stands as the one who introduced this knowledge in the Ottoman Realm and as the intellectual heir to the greatest lettrist of the Islamicate World, Ahmed el-Buni (d. 1225). Τhis paper focuses on the ottoman period and deals with the understandings and interpretations of this particular field of knowledge (‘ilm) from an outside perspective, that is, not through the expert eyes of its practisers, but through those of the polymaths and the people of knowledge. It tackles questions such as the position of cifr among different branches of knowledge, occult and other, as these are presented and analyzed in the various Ottoman encyclopedias, from the early Ottoman period and up until the late 17th century. The starting point of this quest is the opus magnum of Islamicate and Ottoman encyclopedism, Katib Çelebi’s (1609-1657) Keşfü'z-zünun (The Removal of Doubts). In this monumental bibliographic catalog one is presented with the basic literature, characteristics and genealogy of all the branches of knowledge, which were based on the hidden qualities of the letters. The paper seeks to present these different branches and also to highlight the additional role of cifr as a tool in the polymaths’s efforts of understanding and interpreting the natural world.