Definition of "Gill" :

noun: respiratory organ of aquatic animals that breathe oxygen dissolved in water

noun: any of the radiating leaflike spore-producing structures on the underside of the cap of a mushroom or similar fungus

noun: a United States liquid unit equal to 4 fluid ounces

noun: a British imperial capacity unit (liquid or dry) equal to 5 fluid ounces or 142.066 cubic centimeters