Definition of "codpiece"

Borachio: Seest thou not, I say, what a deformed thief this fashion is, how giddily ’a turns about all the hot-bloods between fourteen and five-and-thirty, sometimes fashioning them like Pharaoh’s soldiers in the reechy painting, sometime like god Bel’s priests in the old church-window, sometime like the shaven Hercules in the smirch’d worm-eaten tapestry, where his codpiece seems as massy as his club?

1598–1599 (first performance), William Shakespeare, “Much Adoe about Nothing”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, (please specify the act number in uppercase Roman numerals, and the scene number in lowercase Roman numerals)

On some suits were screwed large iron cod-pieces; these, according to tradition, were intended to prevent the ill consequences of those violent shocks received in charging, either in battle, or at a tournament. Same say, they were meant to contain sponges for receiving the water of knights, who in the heat of an engagement might not have any more convenient method of discharging it. But most probably, they were rather constructed in conformity to a reigning fashion in the make of the breeches of those times.

1786, Francis Grose, A Treatise on Ancient Armour and Weapons, page 21