cocksure

Etymology

Probably from cock + sure, early 16th c.

adj

1. (informal) Too confident; overconfident.
   I thought myself cocksure of his horse, which he readily promis'd me. 1716, Alexander Pope, letter to the Earl of Burlington
   The persistence of the Past is one of those tragicomic blessings which each new age denies, coming cocksure on to the stage to mouth its claim to a perfect novelty. 1906, John Galsworthy, “preface”, in The Man of Property
   These crack specialists, the young scientific fellows, they're so cocksure and so wrapped up in their laboratories that they miss the human element. 1920, Sinclair Lewis, “XXIII”, in Main Street
   Cocksure certainty is the source of much that is worst in our present world, and it is something of which the contemplation of history ought to cure us, not only or chiefly because there were wise men in the past, but because so much that was thought wisdom turned out to be folly – which suggests that much of our own supposed wisdom is no better. I do not mean to maintain that we should lapse into a lazy scepticism. We should hold our beliefs, and hold them strongly. Nothing great is achieved without passion, but underneath the passion there should always be that large impersonal survey which sets limits to actions that our passions inspire. 1954, Bertrand Russell, History as an Art, page 197