spore

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

• noun A small, usually single-celled reproductive body that is resistant to adverse environmental conditions and is capable of growing into a new organism, produced especially by certain fungi, algae, protozoans, and nonseedbearing plants such as mosses and ferns.
• noun A megaspore or microspore.
• noun A dormant nonreproductive body formed by certain bacteria often in response to a lack of nutrients, and characteristically being highly resistant to heat, desiccation, and destruction by chemicals or enzymes.
• intransitive verb To produce spores.

from The Century Dictionary.

• noun A. Middle English form of spur.
• noun In botany, a single cell which becomes free and is capable of developing directly into a new morphologically and physiologically independent individual.
• noun In zoology, the seed or germ of an organism, of minute size, and not of the morphological value of a cell, such as one of the microscopic bodies into which the substance of many protozoans is resolved in the process of reproduction by sporation; a sporule; a gemmule, as of a sponge.
• noun In biology, an organic body of extremely minute size, and not subject to ordinary classification; a sporozoid or zoöspore; a living germ, as a seed of certain diseases.
• noun Figuratively, a germ; a seed; a source of being.

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

• noun One of the minute grains in flowerless plants, which are analogous to seeds, as serving to reproduce the species.
• noun An embryo sac or embryonal vesicle in the ovules of flowering plants.
• noun A minute grain or germ; a small, round or ovoid body, formed in certain organisms, and by germination giving rise to a new organism
• noun One of the parts formed by fission in certain Protozoa. See Spore formation, belw.
• noun (Biol) The formation of reproductive cells or spores, as in the growth of bacilli.

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

• noun A reproductive particle, usually a single cell, released by a fungus, alga, or plant that may germinate into another.
• noun A thick resistant particle produced by a bacterium or protist to survive in harsh or unfavorable conditions.
• verb To produce spores.

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

• noun a small usually single-celled asexual reproductive body produced by many nonflowering plants and fungi and some bacteria and protozoans and that are capable of developing into a new individual without sexual fusion