encyclopedia

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A comprehensive reference work containing articles on a wide range of subjects or on numerous aspects of a particular field, usually arranged alphabetically.

from The Century Dictionary.

• noun The circle of sciences; a general system of instruction in several or all departments of knowledge.
• noun Specifically A work in which the various topics included under several or all branches of knowledge are treated separately, and usually in alphabetical order.
• noun In a narrower sense, a cyclopedia. See cyclopedia
• noun Abbreviated enc., ency., encyc.

from the GNU version of the Collaborative International Dictionary of English.

• noun The circle of arts and sciences; a comprehensive summary of knowledge, or of a branch of knowledge; esp., a work in which the various branches of science or art are discussed separately, and usually in alphabetical order; a cyclopedia.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A comprehensive reference work (often spanning several printed volumes) with in-depth articles (usually arranged in alphabetical order, or sometimes arranged by category) on a range of subjects, sometimes general, sometimes limited to a particular field.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a reference work (often in several volumes) containing articles on various topics (often arranged in alphabetical order) dealing with the entire range of human knowledge or with some particular specialty