organ - a fully differentiated structural and functional unit in an animal that is specialized for some particular function

entrails, innards, viscera - internal organs collectively (especially those in the abdominal cavity); "`viscera' is the plural form of `viscus'"

excretory organ, urinary organ - an organ that separates waste substances from the blood and discharges them

liver - large and complicated reddish-brown glandular organ located in the upper right portion of the abdominal cavity; secretes bile and functions in metabolism of protein and carbohydrate and fat; synthesizes substances involved in the clotting of the blood; synthesizes vitamin A; detoxifies poisonous substances and breaks down worn-out erythrocytes

ticker, heart, pump - the hollow muscular organ located behind the sternum and between the lungs; its rhythmic contractions pump blood through the body; "he stood still, his heart thumping wildly"

stomach, tum, tummy, breadbasket - an enlarged and muscular saclike organ of the alimentary canal; the principal organ of digestion

respiratory organ - any organ involved in the process of respiration

bowel, gut, intestine - the part of the alimentary canal between the stomach and the anus

hindgut - the caudal part of the alimentary canal in vertebrate embryos