Bulb

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late Middle English: via Latin from Greek bolbos ‘onion, bulbous root’.

wiktionary

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From Middle English bulb, bolbe, from Latin bulbus(“bulb, onion”), from Ancient Greek βολβός(bolbós, “plant with round swelling on underground stem”).

etymonline

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bulb (n.)

1560s, "an onion," from French bulbe (15c.), from Latin bulbus "bulb, bulbous root, onion," from Greek bolbos "plant with round swelling on underground stem." Extended 1660s to "spherical underground part of an onion, lily, etc." Expanded by 1800 to "swelling in a glass tube" (thermometer bulb, light bulb, etc.).