Etymology
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arson (n.)

"malicious burning of property," 1670s, from Anglo-French arsoun (late 13c.), Old French arsion, from Late Latin arsionem (nominative arsio) "a burning," noun of action from past participle stem of Latin ardere "to burn," from PIE root *as- "to burn, glow."  The Old English term was bærnet, literally "burning;" and Coke has indictment of burning (1640).

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*as- 

also *es-, Proto-Indo-European root meaning "to burn, glow." 

It forms all or part of: ardent; ardor; area; arid; aridity; aril; arson; ash (n.1) "powdery remains of fire;" azalea; potash; potassium.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit asah "ashes, dust;" Hittite hat- "to dry up;" Greek azein "to dry up, parch," azaleos "dry;" Latin aridus "parched, dry," ārēre "to be dry," āra "altar, hearth;" Armenian azazem "I dry up;" Old English æsce "ash," Old High German asca, Gothic azgo "ashes." 

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