Why is the ninth month called September?
1832, from Modern Latin rhizoma, from Greek rhizoma "mass of tree roots," from rhizoun "cause to strike root, root into the ground, plant," from rhiza "root," probably from PIE *wrad- "branch, root" (cf. Latin radix "root," Old Norse rot "root," Old English wyrt "plant, herb;" see radish).
A plant stem that grows horizontally under or along the ground and often sends out roots and shoots. New plants develop from the shoots. Ginger, iris, and violets have rhizomes. Also called rootstock. Compare bulb, corm, runner, tuber.