cilium

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A microscopic hairlike process extending from the surface of a cell or unicellular organism. Capable of rhythmical motion, it acts in unison with other such structures to bring about the movement of the cell or of the surrounding medium.
• noun An eyelash.
• noun Botany One of the hairs along the margin or edge of a structure, such as a leaf, usually forming a fringe.

from The Century Dictionary.

• noun In anatomy, one of the hairs which grow from the margin of the eyelids; an eyelash.
• noun One of the minute, generally microscopic, hair-like processes of a cell or other part or organ of the body, or of an entire organism, permanently growing upon and projecting from a free surface, capable of active vibratile or ciliary movement, producing currents in surrounding media, as air or water, and thus serving as organs of ingestion or egestion, prehension, locomotion, etc.
• noun In botany: In mosses, one of the hair-like processes within the peristome.
• noun One of the microscopic hair-like appendages which are often present upon the reproductive bodies, such as antherozoids and zoospores of cryptogams. They are frequently two in number and vibrate with great rapidity, producing locomotion.
• noun In entomology, a hair set with others; a fringe, like eyelashes, generally on the leg or margins of the wings of insects.

from the GNU version of the Collaborative International Dictionary of English.

• noun See cilia.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun cytology A hairlike organelle projecting from a eukaryotic cell (such as unicellular organism or one cell of a multicelled organism). These structures serve either for locomotion by moving or as sensors.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a hairlike projection from the surface of a cell; provides locomotion in free-swimming unicellular organisms
• noun any of the short curved hairs that grow from the edges of the eyelids