The scholastic philosopher is interested in definition for a different reason than the lexicographer and linguist. The philosopher is trying to learn things. He defines, after investigating reality, in an attempt to describe reality clearly and to sum up some aspect of his understanding of reality. Hence, we find our scholastic philosophers adopting as a main feature of their method this insistence on defining, on precise and detailed explanation of their definitions, and on proving that their definitions do correctly express what a nature or activity is.This dictionary of the language of scholastic philosophy has been fitted to the needs of beginners and undergraduate students of the subject and has not been previously available in English.This is a reprint of the 1956 edition.