coda n.

c. 1300, "systematic compilation of laws," from Old French code "system of laws, law-book" (13c.), from Latin codex"systematic classification of statutory law," earlier caudex "book," literally "tree trunk," hence, book made up of wooden tablets covered with wax for writing. De Vaan traces this through Proto-Italic *kaud-ek- to PIE *kehu-d- "cleaved, separate," which he also sees as the root of cauda "tail" (see coda).

Meaning "cipher, system of signals and the rules which govern their use" (the sense in secret code) is from 1808. Code-name is from 1879 (in telegraphy). Meaning "system of expressing information and instructions in a form usable by a computer" is from 1946.

"one who lacks courage to meet danger or shrinks from the chance of being hurt," mid-13c., from Anglo-French couard, couart, Old French coart "coward" (no longer the usual word in French, which has now in this sense poltron, from Italian, and lâche), from coe "tail," from Latin coda, popular dialect variant of cauda "tail" (see coda) + -ard, an agent noun suffix denoting one that carries on some action or possesses some quality, with derogatory connotation (see -ard).

The word probably reflects an animal metaphoric sense still found in expressions like turning tail and tail between legs. Coart was the name of the hare in Old French versions of "Reynard the Fox." Italian codardo, Spanish cobarde (Old Spanish couarde) are from French. The spelling in English was influenced by cow (v. and n.).

[S]o strong is the false belief that every bully must be a coward that acts requiring great courage are constantly described as cowardly or dastardly if they are so carried out as not to give the victim a sporting chance; the throwing of a bomb at a king's carriage is much less dastardly than shooting a partridge, because the thrower takes a very real risk .... [Fowler]

As a surname (attested from mid-13c.) it represents Old English cuhyrde "cow-herd." As an adjective, "lacking courage, timorous," from late 13c. Farmer has coward's castle "a pulpit," "Because a clergyman may deliver himself therefrom without fear of contradiction or argument."

late 15c., "band attached to a letter with seals dangling on the free end," from French queue "a tail," from Old French cue, coe, queue, "tail" (12c., also "penis"), from Latin coda (dialectal variant or alternative form of cauda) "tail" (see coda, and compare cue (n.2)).

Also in literal use in 16c. English, "tail of a beast," especially in heraldry. A metaphoric extension to "line of dancers" (c. 1500) perhaps led to the extended sense of "line of people, etc." (1837), but this use in English is perhaps directly from French (queue à queue, "one after another" appears in early 19c. English and American military dictionaries).

If we look now at Paris one thing is too evident: that the Baker's shops have got their Queues, or Tails ; their long strings of purchasers arranged in tail, so that the first come be the first served,—were the shop once open! This waiting in tail, not seen since the early days of July, again makes its appearance in August. In time, we shall see it perfected, by practice to the rank almost of an art ; and the art, or quasi-art, of standing in tail become one of the characteristics of the Parisian People, distinguishing them from all other Peoples whatsoever. [Carlyle, "The French Revolution," 1837]

Also used 18c. in sense of "braid of hair hanging down behind" (attested by 1748), originally part of the wig, in later 18c. of the hair of the head.

QUEUE. From the French, which signifies tail; an appendage that every British soldier is directed to wear in lieu of a club. Regimental tails were ordered be nine inches long. [William Duane, "A Military Dictionary," Philadelphia, 1810]