derring-do

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.). Misspelled derrynge do 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.