From Robert Nares, James Halliwell & Thomas Wright, A Glossary or, Collection of Words, Phrases, Names, and Allusions to Customs, Proverbs, Etc., Which Have Been Thought to Require Illustration (1859):
A DIZARD, DIZZARD, or DISARD. A blockhead, or fool. Probably from the same Saxon etymology as dizzy, dysi. Some have said, from disard, Fr. for a prater, or babbling fellow ; but no such word was ever used in French. Their word is diseur ; nor does the English word mean so much a prater, as a downright dunce, or fool. Thus Cotgrave renders it, not by diseur, or any such word, but by lourdaut.
He that cannot personate the wise man well amongst wisards, let him learn to play the fool well amongst dizzards. G. Chapm., Masque of the Middle Temple, C1.
What a revengeful dizard is this! Lingua, O. P1, v, 165.
Whereat the sergeant wroth, said, Dizzard, calfe, / Thou woud'st if thou hadst wit or sense to see. Harringt., Ep., 2, 9.
{In the old English Homer by Art. Hall (1581), p. 10, which was translated from the French, we have:}
You hereaulter high, come on, quoth he, no daunger dread at all, / For by your disarde king, not you, their wrong on me doth fall.
{The dizard was properly the vice, or fool, in a play ; the jester. This would seem to justify the Fr. derivation.}
[Latin quotation omitted] A dizzard or common vice and jester, counterfetting the gestures of any man, and moving his body as him list. Nomenclator.