tornadon.[From Sp. or Pg. tornar to turn, return, L. tornare to turn, hence, a whirling wind. The Sp. & Pg. tornada is a return. See Turn.] A violent whirling wind; specifically (Meteorol.), a tempest distinguished by a rapid whirling and slow progressive motion, usually accompaned with severe thunder, lightning, and torrents of rain, and commonly of short duration and small breadth; a small cyclone.()n.[NL., fr. L. tornare to turn.] (Zol.) The peculiar free swimming larva of Balanoglossus. See Illust. in Append.()