Green’s Dictionary of Slang

a fool.

[1570		Marriage of Wit and Science II i: Such a cockbraine as thou art I neuer saw the like to it].
1575		‘Mr. S’ Gammer Gurton’s Needle in Whitworth (1997) V ii: He showeth himself herein, ye see, so very a cox.
1821		‘An Amateur’ Real Life in London I 539: Witness thy toast again, — Three C’s; / For who would think that thou by these / Meant Cox, and King, and Curtis!