Definition of cilium in English:


nounPlural cilia

  • 1Biology
    A short microscopic hair-like vibrating structure found 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.

    • ‘Some single-celled organisms called protists do in fact use cilia on their cell surface to swim through water.’
    • ‘As the cilia whip around clockwise, they circulate the fluids.’
    • ‘The cilia create a current by beating in a coordinated manner.’
    • ‘Our respiratory systems are lined with millions of tiny cilia that clean all kinds of irritants - germs, dust, mucus - out of our bodies.’
    • ‘Each hair-like cilium is associated with a set of tubules and structural protein molecules that make up a kinetosome.’
    fibre, thread, strand, tendril
    View synonyms
  • 2Anatomy
    An eyelash.

    • ‘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.