worker

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

• noun One who works at a particular occupation or activity.
• noun One who does manual or industrial labor.
• noun A member of the working class.
• noun A member of a colony of social insects such as ants, bees, wasps, or termites, usually a sterile or sexually immature female but in termites an individual of either sex, that performs specialized work such as building the nest, collecting and storing food, and feeding other members of the colony.

from The Century Dictionary.

• noun One who or that which works; a laborer; a toiler; a performer; a doer.
• noun In entomology, the neuter or undeveloped female of various social hymenopterous and a few other insects, as bees, ants, and termites, which collects pollen, makes honey, builds or fabricates cells or a nest, stores up food, cares for the young, herds and milks the aphids kept as cows, and performs other services for the community of which it is a member.
• noun Maker; creator.
• noun In a carding-machine, one of the urchins, or small card-covered cylinders.
• noun A leather-workers' two-handled knife, used in scraping hides.

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

• noun One who, or that which, works; a laborer; a performer.
• noun (Zoöl.) One of the neuter, or sterile, individuals of the social ants, bees, and white ants. The workers are generally females having the sexual organs imperfectly developed. See Ant, and White ant, under White.

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

• noun A person who performs labor for his living, especially manual labor.
• noun A nonreproductive social insect, such as ant, bee, termite or wasp.
• noun computing A thread performing one instance of a particular task within a program.

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

• noun a member of the working class (not necessarily employed)
• noun a person who works at a specific occupation
• noun sterile member of a colony of social insects that forages for food and cares for the larvae
• noun a person who acts and gets things done