Definition of cilium in US English:


nounPlural cilia

Biology Anatomy
  • 1A short, microscopic, hairlike vibrating structure. Cilia occur in large numbers on the surface of certain cells, either causing currents in the surrounding fluid, or, in some protozoans and other small organisms, providing propulsion.

    • ‘Each hair-like cilium is associated with a set of tubules and structural protein molecules that make up a kinetosome.’
    • ‘Our respiratory systems are lined with millions of tiny cilia that clean all kinds of irritants - germs, dust, mucus - out of our bodies.’
    • ‘The cilia create a current by beating in a coordinated manner.’
    • ‘As the cilia whip around clockwise, they circulate the fluids.’
    • ‘Some single-celled organisms called protists do in fact use cilia on their cell surface to swim through water.’
    fibre, thread, strand, tendril
    View synonyms
    1. 1.1 An eyelash, or a delicate hairlike structure that resembles one.
      • ‘Normally the eyelashes (or cilia) grow from follicles in the eyelid.’
      • ‘Ectopic cilia are particularly irritating and likely to cause corneal ulcers.’


Early 18th century (in the sense ‘eyelash’): from Latin.