The Oxford dictionary of philosophy by Simon Blackburn.

"This bestselling dictionary is written by one of the leading philosophers of our time, and it is widely recognized as the best dictionary of its kind. Comprehensive and authoritative, it covers every aspect of philosophy from Aristotle to Zen. With clear and concise definitions, it provides lively and accessible coverage of not only Western philosophical traditions, but also themes from Chinese, Indian, Islamic, and Jewish philosophy. New entries on philosophy of economics, social theory, neuroscience, philosophy of the mind, and moral conceptions, bring this authoritative third edition up to date. It is the ideal introduction to philosophy for anyone with an interest in the subject, and it is an indispensable work of reference for students and teachers"-- Page 4 of cover.