Source : Webster's Revised Unabridged Dictionary (1913)

Rowdy \Row"dy\, n.; pl. {Rowdies}. [From {Rout}, or Row a
   brawl.]
   One who engages in rows, or noisy quarrels; a ruffianly
   fellow. --M. Arnold.

Source : WordNet®

rowdy
     adj : disturbing the public peace; loud and rough; "a raucous
           party"; "rowdy teenagers" [syn: {raucous}]
     [also: {rowdiest}, {rowdier}]

rowdy
     n : a cruel and brutal fellow [syn: {bully}, {tough}, {hooligan},
          {ruffian}, {roughneck}, {yob}, {yobo}, {yobbo}]
     [also: {rowdiest}, {rowdier}]