Old English mil, from West Germanic *milja (source also of Middle Dutch mile, Dutch mijl, Old High German mila, German meile), from Latin milia "thousands," plural of mille "a thousand" (neuter plural was mistaken in Germanic as a fem. singular), of unknown origin.
The Latin word also is the source of French mille, Italian miglio, Spanish milla. The Scandinavian words (Old Norse mila, etc.) are from English. An ancient Roman mile was 1,000 double paces (one step with each foot), for about 4,860 feet, but there were many local variants and a modern statute mile is about 400 feet longer. In Germany, Holland, and Scandinavia in the Middle Ages, the Latin word was applied arbitrarily to the ancient Germanic rasta, a measure of from 3.25 to 6 English miles. Mile-a-minute (adj.) "very fast" is attested from 1957.