Medical Definition of cilium
plural cilia \-ē-ə\play
2: a minute, short, hairlike process that projects from the surface of most eukaryotic cells, is composed chiefly of microtubules, in unicellular organisms functions chiefly in locomotion, and in higher forms serves especially in the movement of fluids and particles (as the passage of mucus and dust from the lungs) and in sensory reception—see ciliopathy
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