1. (n.) One of the minute grains in flowerless plants, which are analogous to seeds, as serving to reproduce the species.

2. (n.) An embryo sac or embryonic vesicle in the ovules of flowering plants.

3. (n.) A minute grain or germ; a small, round or ovoid body, formed in certain organisms, and by germination giving rise to a new organism; as, the reproductive spores of bacteria, etc.

4. (n.) One of the parts formed by fission in certain Protozoa.

adenovirus aerobe aerobic bacteria amoeba anaerobe anaerobic bacteria bacillus bacteria bacterium basidium bug coccus cystocarp disease-producing microorganism echovirus enterovirus filterable virus fungus germ gram-negative bacteria gram-positive bacteria macrospore megaspore microbe microorganism microsporangium microspore mold nonfilterable virus pathogen picornavirus planospore protozoa protozoon reovirus rhinovirus rickettsia sorus spirillum spirochete sporangium sporocarp sporocyst sporocyte sporophore sporophyte sporule staphylococcus streptococcus swarm spore trypanosome vibrio virus zoospore zygospore