burn (v.) Look up burn at Dictionary.com
12c., combination of Old Norse brenna "to burn, light," and two originally distinct Old English verbs: bærnan "to kindle" (transitive) and beornan "to be on fire" (intransitive), all from Proto-Germanic *brennan/*branajan (cognates: Middle Dutch bernen, Dutch branden, Old High German brinnan, German brennen, Gothic -brannjan "to set on fire"). This perhaps is from PIE *gwher- "to heat, warm" (see warm (adj.)), or from PIE *bhre-n-u, from root *bhreue- "to boil forth, well up" (see brew (v.)). Related: Burned/burnt (see -ed); burning.

Figuratively (of passions, battle, etc.) in Old English. Meaning "cheat, swindle, victimize" is first attested 1650s. In late 18c, slang, burned meant "infected with venereal disease." To burn one's bridges (behind one) "behave so as to destroy any chance of returning to a status quo" (attested by 1892 in Mark Twain), perhaps ultimately is from reckless cavalry raids in the American Civil War. Slavic languages have historically used different and unrelated words for the transitive and intransitive senses of "set fire to"/"be on fire:" for example Polish palić/gorzeć, Russian žeč'/gorel.
burn (n.) Look up burn at Dictionary.com
c.1300, "act of burning," from Old English bryne, from the same source as burn (v.). Until mid-16c. the usual spelling was brenne. Meaning "mark made by burning" is from 1520s. Slow burn first attested 1938, in reference to U.S. movie actor Edgar Kennedy (1890-1948), who made it his specialty.