Algorithm is a man's name that has been mangled twice. It began as al-Khwarizmi, the surname of the ninth-century mathematician from Khwarazm whose works introduced Arabic numerals and sophisticated mathematics to Europe. Medieval Latin turned the name into algorismus, and Middle English had it as algorism, meaning the Arabic numeral system, from the early 1200s.
The th is the second mangling, and it is pure error. In French the word was refashioned as algorithme under the mistaken impression that it had something to do with Greek arithmos, "number." It doesn't — the resemblance is a coincidence — but the fake Greek spelling is what English borrowed in the 1690s and what we are stuck with. The meaning broadened from the Arabic numeral system to any method of computation, and from the middle of the twentieth century it has belonged mostly to computing.
algorithm (n.) 1690s, "Arabic system of computation," from French algorithme , refashioned (under mistaken connection with Greek arithmos "number") from Old French algorisme "the Arabic numeral system" (13c.), from Medieval Latin algorismus , a mangled transliteration of Arabic al-Khwarizmi "native of Khwarazm" (modern Khiva in Uzbekistan), surname of the mathematician whose works introduced sophisticated mathematics to the West (see algebra ). The earlier form in Middle English was algorism (early 13c.), from Old French. The meaning broadened to any method of computation; from mid-20c. especially with reference to computing. also from 1690s
algorithm came in through Later and wider borrowings, and its spelling follows that family's conventions.
How that family writes these sounds
| a technical noun about maths, chemistry, or the stars | Arabic: al- welded onto the front, article and allalgebra, algorithm, alcohol, almanac |
What gives it away on the page
| al- fused to the front of the noun | Arabic, usually via Spanish or Latin — al is the article, stuck on permanently.alcohol, algebra, algorithm, alkali, almanac, admiral |
Placing it without the spelling
| mathematics, chemistry, the stars | Arabic, through Spanish or Latinalgebra, algorithm, alcohol, almanac |
Later and wider borrowings in the spelling guide · guess another word's family