Old English dweorh, dweorg (West Saxon), duerg (Mercian), "very short human being, person much below ordinary stature, whether of proportionate parts or not," also "supernatural being of subhuman size," from Proto-Germanic *dweraz (source also of Old Frisian dwerch, Old Saxon dwerg, Old High German twerg, German Zwerg, Old Norse dvergr), perhaps from PIE *dhwergwhos "something tiny," but with no established cognates outside Germanic.
Also used by c. 1200 of an animal or plant much below the ordinary size of its species." The use of dwarf in the Germanic mythological sense, "a diminished and generally deformed being, dwelling in rocks and hills and skilled in working metals," seems to have faded after Middle English and been revived after c. 1770 from German.
Whilst in this and other ways the dwarfs do at times have dealings with mankind, yet on the whole they seem to shrink from man; they give the impression of a downtrodden afflicted race, which is on the point of abandoning its ancient home to new and more powerful invaders. There is stamped on their character something shy and something heathenish, which estranges them from intercourse with christians. They chafe at human faithlessness, which no doubt would primarily mean the apostacy from heathenism. In the poems of the Mid. Ages, Laurin is expressly set before us as a heathen. It goes sorely against the dwarfs to see churches built, bell-ringing ... disturbs their ancient privacy; they also hate the clearing of forests, agriculture, new fangled pounding-machinery for ore. ["Teutonic Mythology," Jakob Grimm, transl. Stallybrass, 1883]
The shift of the Old English guttural at the end of the word to modern -f is typical (compare enough, draft) and begins to appear early 14c. In Middle English it also was dwerþ, dwerke. Old English plural dweorgas became Middle English dwarrows, later leveled down to dwarfs. The use of dwarves for the legendary race was popularized by J.R.R. Tolkien. As an adjective, from 1590s.
The use of giant and dwarf in reference to stars of the highest and lowest luminosity is attested by 1914, said to have been suggested by Danish astronomer Ejnar Hertzsprung, (1873-1967); hence red dwarf (attested by 1922), white dwarf, black dwarf "dead and lightless star" (1966).
Old English fyr "fire, a fire," from Proto-Germanic *fūr- (source also of Old Saxon fiur, Old Frisian fiur, Old Norse fürr, Middle Dutch and Dutch vuur, Old High German fiur, German Feuer "fire"), from PIE *perjos, from root *paewr- "fire." Current spelling is attested as early as 1200, but did not fully displace Middle English fier (preserved in fiery) until c. 1600.
PIE apparently had two roots for fire: *paewr- and *egni- (source of Latin ignis). The former was "inanimate," referring to fire as a substance, and the latter was "animate," referring to it as a living force (compare water (n.1)).
Brend child fuir fordredeþ ["The Proverbs of Hendyng," c. 1250]
English fire was applied to "ardent, burning" passions or feelings from mid-14c. Meaning "discharge of firearms, action of guns, etc." is from 1580s. To be on fire is from c. 1500 (in fire attested from c. 1400, as is on a flame "on fire"). To play with fire in the figurative sense "risk disaster, meddle carelessly or ignorantly with a dangerous matter" is by 1861, from the common warning to children. Phrase where's the fire?, said to one in an obvious hurry, is by 1917, American English.
Fire-bell is from 1620s; fire-alarm as a self-acting, mechanical device is from 1808 as a theoretical creation; practical versions began to appear in the early 1830s. Fire-escape (n.) is from 1788 (the original so-called was a sort of rope-ladder disguised as a small settee); fire-extinguisher is from 1826. A fire-bucket (1580s) carries water to a fire. Fire-house is from 1899; fire-hall from 1867, fire-station from 1828. Fire company "men for managing a fire-engine" is from 1744, American English. Fire brigade "firefighters organized in a body in a particular place" is from 1838. Fire department, usually a branch of local government, is from 1805. Fire-chief is from 1877; fire-ranger from 1887.
Symbolic fire and the sword is by c. 1600 (translating Latin flamma ferroque absumi); earlier yron and fyre (1560s), with suerd & flawme (mid-15c.), mid fure & mid here ("with fire and armed force"), c. 1200. Fire-breathing is from 1590s. To set the river on fire, "accomplish something surprising or remarkable" (usually with a negative and said of one considered foolish or incompetent) is by 1830, often with the name of a river, varying according to locality, but the original is set the Thames on fire (1796). The hypothetical feat was mentioned as the type of something impossibly difficult by 1720; it circulated as a theoretical possibility under some current models of chemistry c. 1792-95, which may have contributed to the rise of the expression.
[A]mong other fanciful modes of demonstrating the practicability of conducting the gas wherever it might be required, he anchored a small boat in the stream about 50 yards from the shore, to which he conveyed a pipe, having the end turned up so as to rise above the water, and forcing the gas through the pipe, lighted it just above the surface, observing to his friends "that he had now set the river on fire." ["On the Origins and Progress of Gas-lighting," in "Repertory of Patent Inventions," vol. III, London, 1827]