from
The Collaborative International Dictionary of English v.0.48
Tornado \Tor*na"do\, n.; pl. {Tornadoes}. [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.
[1913 Webster]