What does coccus mean?
A coccus (plural: cocci) is a bacterium whose cells are spherical or nearly so, as opposed to rod-shaped bacilli or spiral spirilla. Cocci are classified further by how they arrange themselves after dividing: in pairs (diplococci), in chains (streptococci), or in grape-like clusters (staphylococci). Many familiar and medically important bacteria are cocci, so the term appears constantly in clinical reports, textbooks, and laboratory results, usually qualified by Gram staining characteristics, as in 'gram-positive coccus'. A second, older sense survives in botany, where a coccus denotes a small rounded fruit or one-seeded section of a fruit that resembles a berry. The word comes from the Greek kokkos, meaning grain or berry, via New Latin, and its shape-based logic makes it easy to remember: anything called a coccus looks like a microscopic bead under the lens.
nounA coccus is any spherical or roughly round bacterium. In botany, it can also denote a small rounded fruit or seed resembling a berry.
- Any spherical or ovoid bacterium, occurring singly, in pairs, chains, or clusters.
- A small rounded, berry-like fruit or one-seeded compartment of a fruit (chiefly technical botanical use).
"Under the microscope, the culture revealed chains of tiny cocci characteristic of Streptococcus."
"The lab report identified the infection as caused by gram-positive cocci arranged in clusters."
"Botanists describe each lobe of the castor-oil capsule as containing a single coccus."
The Latin-derived plural 'cocci' is strongly preferred in all medical and scientific usage; pronounced KOK-sigh.
"Gram-positive cocci were observed in short chains on the stained slide."
Every time you hear 'streptococcus' or 'staphylococcus', you're hearing this little word for 'berry' stitched onto another root — and those berry-shaped bacteria are among the most common germs on Earth.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of coccus
Coccus derives from the ancient Greek kokkos, meaning 'grain' or 'berry', which was adopted into New Latin as a generic term before entering English in the early modern period. The same Greek root underlies several other words denoting rounded things, including coccyx (the tailbone) and, more distantly, terms connected to the cochineal insect once prized for red dye. In microbiology the word became established in the nineteenth century alongside bacillus and spirillum as part of the standard vocabulary of bacterial morphology.
Related word forms
How coccus is actually used
The word is technical, appearing almost exclusively in scientific writing — microbiology above all, with an older, rarer sense in descriptive botany. The Latin-style plural 'cocci' (pronounced KOK-sigh) is standard in medical contexts, though the English plural 'cocculses' is not used. In everyday speech it is virtually never encountered except inside compound genus names such as Streptococcus and Staphylococcus.
Easily confused with coccus
The coccyx is the tailbone at the base of the human spine, whereas a coccus is a spherical bacterium — both derive from Greek words for something rounded.