"short, curved, single-edged sword," a characteristic weapon of the Turks and Persians, 1540s, cimiterie, from French cimeterre (15c.) or Italian scimitarra, words of uncertain origin. Turkish would be the expected source of them, but no such word has been found there. Perhaps it is from Persian shimshir (pronounced "shamsher," compare Greek sampsera "a barbarian sword," from Persian), but the OED finds this "unsatisfactory as to form."
The modern spelling is from influence of the Italian form of the word. Century Dictionary (1895) has simitar as preferred spelling, and notes, "This word, owing to its Oriental origin and associations, to ignorance of its original form, and to the imitation now of the F. now of the It. spelling, has appeared in a great variety of forms."
updated on February 02, 2022