gill

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

• noun A ravine.
• noun A narrow stream.
• noun A unit of volume or capacity in the US Customary System, used in liquid measure, equal to ¹/₄ of a pint or four ounces (118 milliliters).
• noun A unit of volume or capacity, used in dry and liquid measure, equal to ¹/₄ of a British Imperial pint (142 milliliters).
• noun A girl, often one's sweetheart.
• noun Zoology The respiratory organ of most aquatic animals that obtain oxygen from water, consisting of a filamentous structure of vascular membranes across which dissolved gases are exchanged.
• noun The wattle of a bird.
• noun Informal The area around the chin and neck.
• noun Botany One of the thin, platelike structures on the underside of the cap of a mushroom or similar fungus.
• intransitive verb To catch (fish) in a gill net.
• intransitive verb To gut or clean (fish).
• intransitive verb To become entangled in a gill net. Used of fish.
• idiom (to the gills) As full as possible; completely.

from The Century Dictionary.

• noun A girl; a sweetheart: used in familiarity or contempt, as either a proper or a common noun.
• noun [Short for gill-creep-by-the-ground, or gillrun-over-the-ground, homely names for the plant, in which gill is a familiar application of the feminine name.] The ground-ivy, Nepeta Glechoma.
• noun Same as gill-beer.
• noun A narrow valley; a ravine, especially one with a rapid stream running through it.
• noun A corrugation or fold; a hollow, as in a sheet of metal.
• noun A fellow or ‘cove’: as, a queer gill.
• noun A frame with a pair of wheels used for conveying timber.
• noun Same as gill-frame.
• noun The breathing-organ of any animal that lives in the water.
• noun Specifically, an organ in aquatic animals for the aërification of the blood through the medium of water; the respiratory apparatus of any animal that breathes the air which is mixed with water; by extension, a branchia, as of any invertebrate and of the ichthyopsidan vertebrates. See branchiæ.
• noun Some part like or likened to a gill.
• noun One of a number of radiating plates on the under side of the cap or pileus of a mushroom.
• noun In entomology, the branchiæ or external breathing-organs of certain insectlarvæ.
• To catch (fish) by the gills, as by means of a gill-net: as, gilled fish.
• [In allusion to the parallel rows of filaments in a fish's gills.] In making worsted yarn, to make the fibers level and parallel with each other by drawing them through a gilling-machine.
• To display the gills in swimming with the head partly out of water: as, mackerel go along gilling.
• noun A liquid measure, one fourth of a pint in the British and United States systems.
• noun A pint of ale.
• noun An English penny or quarter bit.

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

• noun (Anat.) An organ for aquatic respiration; a branchia.
• noun (Bot.) The radiating, gill-shaped plates forming the under surface of a mushroom.
• noun (Zoöl.) The fleshy flap that hangs below the beak of a fowl; a wattle.
• noun The flesh under or about the chin.
• noun (Spinning) One of the combs of closely ranged steel pins which divide the ribbons of flax fiber or wool into fewer parallel filaments.
• noun (Anat.) Same as Branchial arches.
• noun (Anat.) Same as Branchial clefts. See under Branchial.
• noun See Operculum.
• noun (Flax Manuf.) a spreader; a machine for subjecting flax to the action of gills.
• noun a flat net so suspended in the water that its meshes allow the heads of fish to pass, but catch in the gills when they seek to extricate themselves.
• noun (Anat.) an opening behind and below the head of most fishes, and some amphibians, by which the water from the gills is discharged. In most fishes there is a single opening on each side, but in the sharks and rays there are five, or more, on each side.
• noun (Anat.) horny filaments, or progresses, on the inside of the branchial arches of fishes, which help to prevent solid substances from being carried into gill cavities.