DERRING-DO, valour, chivalrous conduct, or "desperate courage," as it is defined by Sir Walter Scott. The word in its present accepted substantival form is a misconstruction of the verbal substantive dorryng or durring, daring, and do or don, the present infinitive of "do," the phrase dorryng do thus meaning "daring to do." It is used by Chaucer in Troylus, and by Lydgate in the Chronicles of Troy. Spenser in the Shepherd's Calendar first adapted derring-do as a substantive meaning "manhood and chevalrie," and this use was revived by Scott, through whom it came into vogue with writers of romance.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)