Book excerpt: The Penguin Dictionary of Psychology has become a byword for demystifying the language of this complex subject. Now fully updated for its fourth edition, this wide-ranging and accessible dictionary is invaluable for both students and professionals, and an indispensable guide to all areas of psychology and psychiatry. -Covers related fields such as neuroscience and social psychology -Describes how terms are employed, their wider connotations and past usage -Looks in detail at such key concepts as addiction and instinct