Webster's Revised Unabridged Dictionary · 1913

Billycock

Billycock , noun

[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

Also: Billycock hat