Microtubular, hairlike structures that some single-celled organisms use for locomotion through liquids. They also cover the cells of certain tissues, such as the epithelium lining the lungs, and help those cells sweep away fluids or particles. Cilia are smaller than flagella.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.

Cilia, the hair which grows from the margin of the eyelids. The term is also applied to microscopic filaments, or plates which project from animal membranes and are endowed with quick vibratile motion. In most of the lower animals the respiratory function is effected by means of the vibratile cilia.

Entry from Everybody's Cyclopedia, 1912.

Cil"i*a (?), n. pl. Cilium, the sing., is rarely used. [L. cilium eyelid.]

1. Anat.

The eyelashes.

2. Biol.

Small, generally microscopic, vibrating appendages lining certain organs, as the air passages of the higher animals, and in the lower animals often covering also the whole or a part of the exterior. They are also found on some vegetable organisms. In the Infusoria, and many larval forms, they are locomotive organs.

3. Bot.

Hairlike processes, commonly marginal and forming a fringe like the eyelash.

4. Zool.

Small, vibratory, swimming organs, somewhat resembling true cilia, as those of Ctenophora.

© Webster 1913.