{ Bil″ly‐cock (?), n., orBil″ly‐cock hat′ (?) }. [Perh. from bully + cock; that is, cocked like the hats of the bullies.] A round, low-crowned felt hat; a wideawake. “The undignified billycocks and pantaloons of the West.” B. H. Chamberlain.
Little acquiesced, and Ransome disguised him in a beard, and a loose set of clothes, and a billicock hat. Charles Reade.