The clavis sanationis was written in the thirteenth century by Simon of Genoa, a physician to pope Nicolas IV. It is a multilingual dictionary that covers medical terminology in Latin, Greek and Arabic language. It uses, and often quotes, a number of valuable sources which are otherwise lost today.
Most entries would have the following structure: "The disease/plant v is called w in Arabic and x in Greek. According to source y it is defined by z". In several cases, source y was lost in the course of the centuries.
The clavis' most obvious value is its helpfulness in reconstructing lost sources. Also, it allows us to understand which type of content was considered relevant at the time, and which sources Simon had at his disposal. Moreover, the text yields large amounts of new lexicographical material. It may be seen as a missing link that will help us to connect the Latin, Greek and Arabic tradition.
For further information on the historical context, please see this entry.