(pl. tetrabrachii) a person born with a severe malformation, having four arms. [After scientific Latin tetrabrachius (1861 or earlier) < tetra-tetra-comb. form + ancient Greek βραχίων arm (see brachio-cephalicadj.).]
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1890 J. S. BillingsNational Med. Dict. II. 659/2Tetrabrachius, a monster having four arms.