"hub of a cart-wheel," Middle English, from Old English nafa, nafu, from Proto-Germanic *nabo- (source also of Old Saxon naba, Old Norse nöf, Middle Dutch nave, Dutch naaf, Old High German naba, German Nabe), perhaps connected with the root of navel on notion of centrality (compare Latin umbilicus "navel," also "the end of a roller of a scroll;" Greek omphalos "navel," also "the boss of a shield").

royal officer, especially one charged with care of horses, 1590s, short for groom of the equirrie, from esquiry "stables" (1550s), from French escuerie (Modern French écurie), perhaps from Medieval Latin scuria "stable," from Old High German scura "barn" (German Scheuer); or else from Old French escuier "groom," from Vulgar Latin *scutarius "shield-bearer." In either case, the spelling was influenced by Latin equus "horse," which is unrelated.

also saltier, c. 1400, sautour, an ordinary that resembles a St. Andrew's Cross on a shield or flag, consisting of a bend dexter and a bend sinister crossing each other, from Old French sautoir, sautour, literally "stirrup," and directly from Medieval Latin saltarium, noun use of neuter of Latin saltatorius "pertaining to leaping," from salire "to leap" (see salient (adj.)). The connection between stirrups and the diagonal cross is said to be the two deltoid shapes that comprise the cross.

1560s, "pertaining to or situated on the right hand," from Latin dexter "on the right hand" (source also of French dextre, Spanish diestro, Italian destro),  from PIE root *deks- "right, opposite of left; south." The Latin form is with the comparative suffix -ter, thus meaning etymologically "the better direction." Middle English dester meant "right hand," and compare destrier. In heraldry, the part of the shield which is to the right when fitted on the arm, hence the side of the field to the left of the spectator.

"very venomous snake of Egypt," 1520s, earlier aspis (mid-14c.), from Old French aspe "asp" (13c.) or directly from Latin aspidem (nominative aspis), from Greek aspis "an asp, Egyptian viper," literally "a round shield;" the serpent so called probably in reference to its neck hood. As to the etymology of the Greek word, Beekes finds that "No remotely convincing suggestions have been made." The name was subsequently applied to the common vipers and adders of Europe, which however are only slightly venomous.

"powdery remains of fire," Old English æsce "ash," from Proto-Germanic *askon (source also of Old Norse and Swedish aska, Old High German asca, German asche, Middle Dutch asche, Gothic azgo "ashes"), from PIE root *as- "to burn, glow." Spanish and Portuguese ascua "red-hot coal" are Germanic loan-words.

An ancient symbol of grief or repentance; hence Ash Wednesday (c. 1300), from custom introduced by Pope Gregory the Great of sprinkling ashes on the heads of penitents on the first day of Lent. Ashes meaning "mortal remains of a person" is late 13c., in reference to the ancient custom of cremation. Meaning "Finely pulverized lava thrown from a volcano" is from 1660s.

early 15c. as the national emblem of England (St. George's Cross), also the badge of the Order of the Temple. Hence red-cross knight, one bearing such a marking on shield or crest. In 17c., a red cross was the mark placed on the doors of London houses infected with the plague. The red cross was adopted as a symbol of ambulance service in 1864 by the Geneva Conference, and the Red Cross Society (later also, in Muslim lands, Red Crescent) philanthropic organization was founded to carry out the views of the 1864 conference as well as other works of relief.

1610s, "bowl-shaped mouth of a volcano," from a specialized use of Latin crater, from Greek krater "large bowl from which red wine mixed with water was served to guests," from kera- "to mix," from PIE root *kere- "to mix, confuse; cook" (see rare (adj.2)).

The extension to volcanoes began in Latin. The literal classical sense is attested in English from 1730. Applied to asteroid scars on the moon since 1831 (they originally were thought to be volcanic) and later extended to other planets. Meaning "cavity formed by the explosion of a military mine" is from 1839. The Battle of the Crater in the U.S. Civil War was July 30, 1864.

As a verb, "having a crater or craters," by 1848 in poetry, 1872 in scientific writing. Related: Cratered; cratering.