bacteria
n.-
1 microorganisms (n.) B2 Upper Intermediate Sciencetiny living things that can only be seen with a microscope.
microscopic single-celled organisms that exist in diverse environments. Technically the plural of 'bacterium', though frequently used as a collective noun in non-scientific contexts.
ExampleYou should wash your hands to get rid of any harmful bacteria.
ExampleThe researchers identified several strains of bacteria in the soil that were capable of breaking down plastic waste.
UsageUsually plural; takes a plural verb in formal and academic writing.
PitfallThis bacteria is very dangerous.These bacteria are very dangerous.In formal and scientific writing, 'bacteria' is plural. Use 'bacterium' for a single organism.
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2 a lowlife person (n.) C2 Proficiency Slang Vulgara very rude or unpleasant person who is treated with no respect.
a derogatory term for a person or group of people perceived as socially or morally inferior.
ExampleHe treated the waiters like they were just bacteria.
ExampleThe corrupt official looked down on the protesters as if they were mere bacteria infecting his city.
Teacher's tipThis is a highly offensive and dehumanising insult; learners should recognise it but avoid using it.
Borrowed from New Latin bacteria, plural of bactērium, from Ancient Greek βακτήριον (baktḗrion, “little rod”).
From New Latin bactēria, from Ancient Greek βακτηρίᾱ (baktēríā, “rod, stick”).
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.
Last updated June 19, 2026