The Collaborative International Dictionary of English v.0.48:

Cocky \Cock"y\, a. [See Cocket.]
   Pert. [Slang]
   [1913 Webster] Cockyolly

WordNet (r) 3.0 (2006):

cocky
    adj 1: overly self-confident or self-assertive; "a very cocky
           young man"

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "cocky":
   aggressively self-confident, arrogant, audacious, biggety, bluff,
   bold, brash, brassy, brazen, bumptious, challenging, cheeky,
   chesty, chutzpadik, cocksure, conceited, contemptuous, crusty,
   daring, defiant, defying, derisive, disdainful, disregardful,
   disrespectful, egotistical, facy, flip, flippant, fresh, gally,
   gratuitous, greatly daring, haughty, immodest, impertinent,
   impudent, insolent, know-it-all, malapert, nervy, obtrusive,
   overconfident, overwise, peacockish, peacocky, perk, perky, pert,
   prideful, proud, puffed up, regardless of consequences, rude,
   sassy, saucy, self-conceited, self-important, self-opinionated,
   smart, smart-alecky, smart-ass, stuck-up, swelled-headed,
   uncalled-for, vain, wise-ass