Definitions of micro-organism
  1. noun
    any organism of microscopic size
    synonyms: microorganism
    see moresee less
    show 34 types...
    hide 34 types...
    (biology) a single-celled microorganism (especially a flagellate protozoan)
    intestinal flora
    harmless microorganisms (as Escherichia coli) that inhabit the intestinal tract and are essential for its normal functioning
    (virology) ultramicroscopic infectious agent that replicates itself only within cells of living hosts; many are pathogenic; a piece of nucleic acid (DNA or RNA) wrapped in a thin coat of protein
    moneran, moneron
    organisms that typically reproduce by asexual budding or fission and whose nutritional mode is absorption or photosynthesis or chemosynthesis
    bacteria, bacterium
    (microbiology) single-celled or noncellular spherical or spiral or rod-shaped organisms lacking chlorophyll that reproduce by fission; important as pathogens and for biochemical properties; taxonomy is difficult; often considered to be plants
    bug, germ, microbe
    a minute life form (especially a disease-causing bacterium); the term is not in technical use
    any disease-producing agent (especially a virus or bacterium or other microorganism)
    any of the unicellular protists
    protist, protistan
    free-living or colonial organisms with diverse nutritional and reproductive modes
    microscopic plants; bacteria are often considered to be microflora
    arborvirus, arbovirus
    a large heterogeneous group of RNA viruses divisible into groups on the basis of the virions; they have been recovered from arthropods, bats, and rodents; most are borne by arthropods; they are linked by the epidemiologic concept of transmission between vertebrate hosts by arthropod vectors (mosquitoes, ticks, sandflies, midges, etc.) that feed on blood; they can cause mild fevers, hepatitis, hemorrhagic fever, and encephalitis
    bacteriophage, phage
    a virus that is parasitic (reproduces itself) in bacteria
    plant virus
    a plant pathogen that is a virus consisting of a single strand of RNA
    animal virus
    an animal pathogen that is a virus
    slow virus
    a virus that remains dormant in the body for a long time before symptoms appear
    archaebacteria, archaebacterium, archaeobacteria, archeobacteria
    considered ancient life forms that evolved separately from bacteria and blue-green algae
    acidophil, acidophile
    an organism that thrives in a relatively acid environment
    probiotic, probiotic bacterium, probiotic flora, probiotic microflora
    a beneficial bacterium found in the intestinal tract of healthy mammals; often considered to be a plant
    a rodlike bacterium (especially any of the rod-shaped or branched bacteria in the root nodules of nitrogen-fixing plants)
    eubacteria, eubacterium, true bacteria
    a large group of bacteria having rigid cell walls; motile types have flagella
    Calymmatobacterium, genus Calymmatobacterium
    a genus of bacterial rods containing only the one species that causes granuloma inguinale
    Francisella, genus Francisella
    a genus of Gram-negative aerobic bacteria that occur as pathogens and parasite in many animals (including humans)
    Neisseria gonorrhoeae, gonococcus
    the pus-producing bacterium that causes gonorrhea
    tumor virus
    a cell-free filtrate held to be a virus responsible for a specific neoplasm
    (genetics) a virus or other agent that is used to deliver DNA to a cell
    Legionella pneumophilia, legionella
    the motile aerobic rod-shaped Gram-negative bacterium that thrives in central heating and air conditioning systems and can cause Legionnaires' disease
    any of the bacteria in the soil that take part in the nitrogen cycle; they oxidize ammonium compounds into nitrites or oxidize nitrites into nitrates
    penicillin-resistant bacteria
    bacteria that are unaffected by penicillin
    pus-forming bacteria
    bacteria that produce pus
    any rod-shaped bacterium
    Gram-positive bacteria usually occurring in pairs
    protozoan, protozoon
    any of diverse minute acellular or unicellular organisms usually nonphotosynthetic
    alga, algae
    primitive chlorophyll-containing mainly aquatic eukaryotic organisms lacking true stems and roots and leaves
    a strain of bacteria that is resistant to all antibiotics
    type of:
    being, organism
    a living thing that has (or can develop) the ability to act or function independently
Word Family

Test prep from the experts

Boost your test score with programs developed by’s experts.

  • Proven methods: Learn faster, remember longer with our scientific approach.
  • Personalized plan: We customize your experience to maximize your learning.
  • Strategic studying: Focus on the words that are most crucial for success.


  • Number of words: 500+
  • Duration: 8 weeks or less
  • Time: 1 hour / week


  • Number of words: 500+
  • Duration: 10 weeks or less
  • Time: 1 hour / week


  • Number of words: 700+
  • Duration: 10 weeks
  • Time: 1 hour / week