Etymology
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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.
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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.
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incendiarism (n.)
1670s; see incendiary + -ism. Originally figurative; the literal sense of "malicious burning" is attested from 1755.
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incense (v.1)
early 15c., encensen "to arouse, inspire," from Old French incenser, from Latin incensare, frequentative of incendere "set on fire," figuratively "incite, enrage, rouse" (see incendiary). From mid-15c. as "to provoke, anger." Literal sense "to heat, make (something) hot" is from c. 1500 in English but is rare.
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incense (n.)
late 13c., "gum or other substance producing a sweet smell when burned," from Old French encens (12c.), from Late Latin incensum "burnt incense," literally "that which is burnt," noun use of neuter past participle of Latin incendere "set on fire" (see incendiary). Meaning "smoke or perfume of incense" is from late 14c.
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*kand- 
also *kend-, Proto-Indo-European root meaning "to shine."

It forms all or part of: candela; candelabrum; candescent; candid; candidate; candle; candor; chandelier; chandler; frankincense; incandescence; incandescent; incendiary; incense (n.) "substance producing a sweet smell when burned;" incense (v.1) "to provoke, anger."

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit cand- "to give light, shine," candra- "shining, glowing, moon;" Greek kandaros "coal;" Latin candere "to shine;" Welsh cann "white," Middle Irish condud "fuel."
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firebug (n.)
also fire-bug, "arsonist, incendiary," 1869, from fire (n.) + bug (n.) in the "obsessed person" sense.
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petroleur (n.)

"an incendiary," especially one of the adherents of the Commune who used petroleum to set fire to the public buildings of Paris upon the entry of the national troops, 1871, from French pétroleur, from petrole (see petrol). The fem. form is pétroleuse.

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napalm (n.)

1942, from naphthenic + palmitic, names of the two acids used in manufacture of the chemical thickening agent. See naphtha. It was used especially in mixture with gasoline to make a kind of inflammabvle jelly used in flame-throwers, incendiary bombs, etc. The verb, "to destroy with napalm," is by 1950, from the noun. Related: Napalmed; napalming.

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incentive (n.)
early 15c., "that which moves the mind or stirs the passion," from Late Latin incentivum, noun use of neuter of Latin adjective incentivus "setting the tune" (in Late Latin "inciting"), from past participle stem of incinere "strike up," from in- "in, into" (from PIE root *en "in") + canere "to sing" (from PIE root *kan- "to sing"). The sense apparently was influenced in Late Latin by association with incendere "to kindle." (Milton uses the adjective to mean "setting fire, incendiary.") Meaning "rewards meant to encourage harder work" is from 1948, short for incentive payment, etc. (see incentive (adj.)).
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