cirrus

noun

Etymology: 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.

1. Synonym of tendril (“a thin, spirally coiling stem that attaches a plant to its support”).

   “Cirri are taken for thoſe fine Strings, or Hairs, by vvhich ſome Plants faſten themſelves, in order to their Support in creeping along; as Ivy, &c.”

2. A thin tendril-like appendage, such as a barbel (“whisker-like sensory organ around the mouth”) of some fish, a cilium of some species of protists, or a foot of some crustaceans of the infraclass Cirripedia.

   “Each foot is divided into two parts, one dorsal, the other ventral, and each part has a bundle of subulate bristles and a cirrus.”

   “All creatures which have their skins protected, whether by feathers, or shells, or scales, have an exquisite touch in their mouth, or in the appendages which hang from it. Fishes have cirri which hang from their mouth, and these are equivalent to the feelers or tentacula of insects and crustaceans.”

3. A principal high-level type of cloud, typically composed of thin, delicate, white filaments or wisps, or narrow bands.

   “[page 99] Cirrus. […] Parallel, flexuous, or diverging fibres, extensible in any or in all directions. […] [page 100] In fair weather, with light variable breezes, the sky is seldom quite clear of small groups of the oblique cirrus, which frequently come on from the leeward, and the direction of their increase is to windward.”

   “Cirrus clouds moving from the southwest indicate falling temperature; moving from the northwest they indicate the probability of rising temperature. They are the mares' tales and cattails of sailors' cant. Near the horizon, cirrus clouds may have a stratiform appearance.”