What does flagellum mean?
A flagellum is a long, slender, whiplike appendage that extends from the surface of many microorganisms — most famously bacteria — as well as from sperm cells. By rotating like a corkscrew or sweeping in waves, the flagellum drives the cell through water and other fluids, making it one of nature's principal solutions to microscopic locomotion. The word comes from the Latin 'flagellum', meaning a whip or scourge, and that figurative ancestry remains apt: under a microscope these structures lash and thrash with striking whip-like motion. Flagellum belongs firmly to scientific register; general readers meet it in biology writing rather than everyday conversation. Its plural, 'flagella', appears constantly in the literature, and related terms such as 'flagellate' and 'flagellation' share the same root. The structure's remarkable efficiency has made it a celebrated example of biological machinery, studied intensively since the earliest days of microscopy.
nounA long, whiplike appendage that projects from certain cells or microorganisms, such as bacteria and sperm cells, whose rhythmic beating propels the organism through a liquid medium. In historical usage, it can also denote a whip or scourge used for flogging.
- A long, whiplike cellular appendage used by microorganisms and reproductive cells for locomotion through fluid.
- A whip or scourge used for flogging (historical or technical use).
"The bacterium swam toward the nutrient source by rotating its flagellum like a corkscrew."
"Each sperm cell drives itself forward by lashing its single flagellum."
"Under the microscope, the bacterium's flagellum appeared as a fine, undulating filament trailing behind the cell."
The plural 'flagella' follows the Latin pattern and is strongly preferred in scientific contexts; 'flagellums' is an anglicized alternative but less common. Cells typically bear one or several flagella, so the plural appears frequently in descriptive writing.
"Many bacteria are propelled by one or more flagella anchored in their cell membrane."
Some bacteria spin their flagella at up to around 1,000 revolutions per second — a biological rotary motor built from protein.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of flagellum
The word flagellum derives directly from Latin 'flagellum', meaning 'a small whip' or scourge, a diminutive form associated with 'flagrum', a heavier lash used in Roman floggings. English adopted the term in the early nineteenth century as biologists described the whip-like filaments they observed on microscopic organisms. The same Latin root produced cognates such as 'flagellant', 'flagellate', and 'flagellation', all connected to whipping or lashing motion, which suits both the word's literal origin and its modern biological sense.
Related word forms
How flagellum is actually used
Flagellum is overwhelmingly a scientific term, encountered mainly in microbiology and cell biology texts; the plural 'flagella' is standard in scholarly writing, though 'flagellums' is acceptable. The older sense referring to an actual whip survives chiefly in historical discussions of Roman punishment or in religious contexts surrounding self-flagellation.
Easily confused with flagellum
A cilium is generally shorter and beats in coordinated oar-like strokes, whereas a flagellum is longer and moves with wave-like or rotating motion.