Definition of cilium in US English:



  • 1Biology
    A short microscopic hairlike 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.’
    • ‘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.’
    • ‘As the cilia whip around clockwise, they circulate the fluids.’
    • ‘The cilia create a current by beating in a coordinated manner.’
    fibre, thread, strand, tendril
    View synonyms
  • 2Anatomy
    An eyelash.

    • ‘Ectopic cilia are particularly irritating and likely to cause corneal ulcers.’
    • ‘Normally the eyelashes (or cilia) grow from follicles in the eyelid.’


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