noun
(zoology) A specialized cell, group of cells, or organ of endothelial origin in the human or animal body that synthesizes a chemical substance, such as hormones or breast milk, and releases it, often into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland).
(botany) A secretory structure on the surface of an organ.
noun
(mechanics) A compressable cylindrical case and its contents around a shaft where it passes through a barrier, intended to prevent the passage of a fluid past the barrier, used for example around a ship’s propeller shaft or around a tap, valve or faucet.