A gill is the body part that helps a fish breathe underwater. In fish and other aquatic creatures, their gills are equivalent to our lungs.

Fish and some amphibians need to breathe the oxygen in water to live, and they use their gills for this. Gills are the main organs of respiration for animals that live in or under the water. The root of gill is uncertain, but it may be related to the Old Norse gjölnar, "gills," and rooted in the Proto-Indo-European ghel-una, or "jaw."

Definitions of gill
  1. noun
    respiratory organ of aquatic animals that breathe oxygen dissolved in water
    synonyms: branchia
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    comb-like respiratory structure serving as the gill of certain mollusks
    one of the often brightly colored and branching hornlike structures on the back of the nudibranch (and other related mollusks) that serve as gills
    external gill
    occurs in some mollusks and in tadpoles and other immature amphibians
    type of:
    respiratory organ
    any organ involved in the process of respiration
  2. noun
    any of the radiating leaflike spore-producing structures on the underside of the cap of a mushroom or similar fungus
    synonyms: lamella
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    type of:
    plant organ
    a functional and structural unit of a plant or fungus
  3. noun
    a United States liquid unit equal to 4 fluid ounces
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    type of:
    United States liquid unit
    a liquid unit officially adopted in the United States Customary System
  4. noun
    a British imperial capacity unit (liquid or dry) equal to 5 fluid ounces or 142.066 cubic centimeters
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    type of:
    British capacity unit, Imperial capacity unit
    a unit of measure for capacity officially adopted in the British Imperial System; British units are both dry and wet
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