Tornado is a Spanish word that English got wrong twice. It is probably a mangled borrowing of Spanish tronada, "thunderstorm," from tronar, "to thunder." English navigators had it in the 1550s as ternado for a violent squall in the tropical Atlantic.
Then two things happened. The r and the o swapped places, probably under the influence of a different Spanish word, tornar, "to twist, to turn" — which suited a whirling storm so well that the folk etymology stuck. And the final -a became -o, which the Century Dictionary explains bluntly: English changed Spanish terminal -a to -o "to give the word a more Spanish look." So the modern spelling is a Spanish word reshaped by an English guess about what Spanish ought to look like. The sense of a violent rotating funnel cloud dates from the 1620s.
tornado (n.) 1550s, ternado , navigator's word for a small, violent, windy thunderstorm in the tropical Atlantic, probably a mangled borrowing from Spanish tronada "thunderstorm," from tronar "to thunder," from Latin tonare "to thunder" (see thunder (n.)). In 17c. English also spelled tornatho , tornathe , turnado ; the modern spelling is by 1620s. The metathesis of -o- and -r- probably is by influence of Spanish tornar "to twist, turn" (from Latin tornare "to turn"). The change of Spanish terminal -a to -o in English was common, "to give the word a more Spanish look" [Century Dictionary]. The meaning "extremely violent whirlwind" is attested by 1620s; specifically as "destructive rotary funnel cloud," usually pendent from a mass of black cloud, especially in the U.S. Midwest, is by 1849. Related: Tornadic; tornadoed . also from 1550s
tornado came in through Later and wider borrowings, and its spelling follows that family's conventions.
How that family writes these sounds
| an unstressed vowel ending a word about food or music | Italian or Spanish: -o, -a, -ipiano, opera, spaghetti, tornado |
What gives it away on the page
| -o/-a endings, ll, rr, ny for ñ | Spanish — much of it from the Americas.tornado, cargo, plaza, armadillo, guerrilla, canyon, mosquito |
Placing it without the spelling
| the Americas — ranching, weather, food | Spanishtornado, canyon, chocolate, tomato |
| an unstressed vowel on the end, in food, music, or weather | Italian or Spanishpiano, opera, tornado, cargo |
Later and wider borrowings in the spelling guide · guess another word's family