Ramus

google

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mid 17th century: from Latin, literally ‘branch’.

wiktionary

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Borrowed from Latin rāmus(“branch”).

etymonline

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ramus (n.)

in anatomy, "a branch or branching part," 1803, from Latin ramus "a branch, bough, twig," from earlier *radmo- and cognate with radix "root," from PIE root *wrād- "branch, root." This is the old reconstruction, which de Vaan, after some hesitation, finds justified. Related: Ramulous; ramulose.