The Collaborative International Dictionary of English v.0.48:

Cowboy \Cow"boy`\ (-boi`), n.
   1. A cattle herder; a drover; specifically, one of an
      adventurous class of herders and drovers on the plains of
      the Western and Southwestern United States.
      [1913 Webster]

   2. One of the marauders who, in the Revolutionary War
      infested the neutral ground between the American and
      British lines, and committed depredations on the
      Americans.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

cowpoke \cowpoke\ n.
   a hired hand who tends cattle and performs other duties on
   horseback; -- an informal name for cowboy.

   Syn: cowboy, cowpuncher, puncher, cowman, cattleman, cowhand,
        cowherd.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

cowboy
    n 1: a hired hand who tends cattle and performs other duties on
         horseback [syn: cowboy, cowpuncher, puncher,
         cowman, cattleman, cowpoke, cowhand, cowherd]
    2: a performer who gives exhibitions of riding and roping and
       bulldogging [syn: cowboy, rodeo rider]
    3: someone who is reckless or irresponsible (especially in
       driving vehicles)

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "cowboy":
   broncobuster, buckaroo, caballero, cattleman, cavalier, cavalryman,
   chevalier, circus rider, cowgirl, cowhand, cowherd, cowman,
   cowpuncher, drover, equestrian, equestrienne, gaucho, goatherd,
   gooseboy, gooseherd, herder, herdsman, hogherd, horse soldier,
   horse wrangler, horseback rider, horsebacker, horseherd, horseman,
   horsewoman, jockey, knight, mounted policeman, pigman, postboy,
   postilion, puncher, rider, roughrider, sheepherder, sheepman,
   shepherd, shepherdess, steeplechaser, swanherd, swineherd,
   trick rider, vaquero, waddy, wrangler



The Jargon File (version 4.4.7, 29 Dec 2003):

cowboy
 n.

    [Sun, from William Gibson's cyberpunk SF] Synonym for hacker. It is
    reported that at Sun this word is often said with reverence.


The Free On-line Dictionary of Computing (30 December 2018):

cowboy

   [Sun, from William Gibson's cyberpunk SF]  Synonym
   for hacker.  It is reported that at Sun this word is often
   said with reverence.

   [Jargon File]