Incendiary
late Middle English: from Latin incendiarius, from incendium ‘conflagration’, from incendere ‘set fire to’.
wiktionary
From Middle English incendiarie, from Old French incendiaire, from Latin incendiārius(“setting alight”), from incendium(“destructive fire”), from incendō(“I set on fire, kindle”), from in-(“into, in, on, upon”) + candeō(“I am hot”).
etymonline
incendiary (n.)
c. 1400, "person who sets malicious fires," from Latin incendiarius "an incendiary," literally "causing a fire" (see incendiary (adj.)). Meaning "person who enflames political passions" is from 1630s.
incendiary (adj.)
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.
