"Exhaustively researched and thoroughly revised, the Fifth Edition contains 10,000 new words and senses, over 4,000 dazzling new full-color images, and authoritaive, up-to-date guidance on usage from the celebrated American Heritage Usage Panel. Thousands of definitions have been revised in rapidly changing fields such as astronomy and biology, geographical entries and maps have been completely updated, and the dictionary's signature feature notes on word history, synonymy, and language variation have been enhanced and improved. Trustworthly advice on controversies and conundrums in English usage is provided by the American Heritage Usage Panel, a group of 200 prominent users of the language."--Book jacket.