The Collaborative International Dictionary of English v.0.48:

Runaway \Run"a*way`\, n.
   1. One who, or that which, flees from danger, duty,
      restraint, etc.; a fugitive.
      [1913 Webster]

            Thou runaway, thou coward, art thou fled? --Shak.
      [1913 Webster]

   2. The act of running away, esp. of a horse or teams; as,
      there was a runaway yesterday.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Runaway \Run"a*way`\, a.
   1. Running away; fleeing from danger, duty, restraint, etc.;
      as, runaway soldiers; a runaway horse.
      [1913 Webster]

   2. Accomplished by running away or elopement, or during
      flight; as, a runaway marriage.
      [1913 Webster]
      [1913 Webster]

WordNet (r) 3.0 (2006):

runaway
    adj 1: completely out of control; "runaway inflation"
    n 1: an easy victory [syn: runaway, blowout, romp,
         laugher, shoo-in, walkaway]
    2: someone who flees from an uncongenial situation; "fugitives
       from the sweatshops" [syn: fugitive, runaway, fleer]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "runaway":
   DP, absconder, at large, bolter, breather, cakewalk, cinch,
   conquest, deserter, disappearing, disengaged, displaced person,
   easy, effortless, eloper, emigre, escaped, escapee, evacuee, fled,
   fleer, flown, free, fugitive, hot, in flight, loose, on the lam,
   on the loose, out of, overwhelming, pushover, rampant, refugee,
   renegade, romp, rout, runagate, scot-free, setup, skedaddler,
   stateless person, triumph, truant, unchecked, uncontested,
   uncontrolled, unsuppressed, victory, walkaway, walkover,
   well out of, wild, win