Etymology
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endo- 

word-forming element meaning "inside, within, internal," from Greek endon "in, within" (from PIE *en-do-, extended form of root *en "in").

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adeno- 

scientific word-forming element meaning "gland," from Greek adēn "gland," probably from a suffixed form of PIE root *engw- "groin; internal organ" (source also of Latin inguen "groin;" see inguinal).

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