cirrus

Learned borrowing from Latin cirrus (“curl; fringe of clothes; mane (especially forelock) of a horse; etc”); further etymology unknown.

Sense 2 (“type of cloud”) was coined by the British chemist and amateur meteorologist Luke Howard (1772–1864): see the 1803 quotation.

The plural form cirri is also a learned borrowing from Latin cirrī, the nominative or vocative plural of cirrus.