"empyreal," mid-14c. (as empyre), probably via Medieval Latin empyreus, from Greek empyros "fiery," from assimilated form of en (see en- (2)) + pyr "fire" (from PIE root *paewr- "fire"). As an adjective in English from early 15c. The etymological sense is "formed of pure fire or light." In ancient Greek cosmology, the highest heaven, the sphere of pure fire; later baptized with a Christian sense of "abode of God and the angels."
1540s, "action of applying fire or setting on fire," verbal noun from fire (v.). From c. 1600 as "act of discharging firearms." Firing squad is attested from 1891 in reference to military executions; earlier as "those selected to fire over the grave of anyone interred with military honors" (1864); earlier in both senses is firing-party (1798 in reference to military executions; 1776 in reference to military funerals).
mid-15c., "capable of being used to set fires," from Latin incendiarius "causing a fire," from incendium "a burning, a fire, conflagration," from incendere "set on fire, light up with fire, brighten," figuratively, "incite, rouse, excite, enrage," from in- "into, in, on, upon" (from PIE root *en "in") + candere "to shine, glow, be on fire" (from PIE root *kand- "to shine").
Figurative sense of "enflaming passions" is from 1610s in English. Meaning "relating to criminal burning" is from 1610s. Military use, of bombs, shells, etc., attested from 1871. The obsolete poetic verb incend is attested from c. 1500.
early 15c., in pathology, "excessive redness or swelling in a body part," from Old French inflammation (14c.) and directly from Latin inflammationem (nominative inflammatio) "a kindling, a setting on fire," noun of action from past participle stem of inflammare "to set on fire" (see inflame). Literal sense "act of setting on fire" in English is from 1560s.