guild

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

• noun An association of persons of the same trade or pursuits, formed to protect mutual interests and maintain standards.
• noun A similar association, as of merchants or artisans, in medieval times.
• noun Ecology A group of species in a community that use similar environmental resources in a similar way, such as a group of songbirds that all glean insects from leaves.

from The Century Dictionary.

• An obsolete spelling of gild.
• etc. See gild, etc.

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

• noun An association of men belonging to the same class, or engaged in kindred pursuits, formed for mutual aid and protection; a business fraternity or corporation. They were originally licensed by the government, and endowed with special privileges and authority.
• noun obsolete A guildhall.
• noun A religious association or society, organized for charitable purposes or for assistance in parish work.

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

• noun A group of tradespeople made up of merchants, craftspeople, or artisans, particularly in the Middle Ages
• noun biology A group of diverse species that share common characteristics or habits

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

• noun a formal association of people with similar interests