derring-do (n.)

"daring deeds, daring action," 1570s, originally (late 14c.) dorrying don, literally "daring (to) do," from durring "daring," present participle of Middle English durren "to dare" (see dare (v.)) + don, infinitive of do (v.). Chaucer used it in passages where the sense was "daring to do" (what is proper to a brave knight). Misspelled derrynge do in 1500s and mistaken for a noun by Spenser, who took it to mean "manhood and chevalrie;" picked up from him and passed on to Romantic poets as a pseudo-archaism by Sir Walter Scott.