The Collaborative International Dictionary of English v.0.48:

Scapegrace \Scape"grace`\, n.
   A graceless, unprincipled person; one who is wild and
   reckless. --Beaconsfield.
   [1913 Webster]

WordNet (r) 3.0 (2006):

scapegrace
    n 1: a reckless and unprincipled reprobate [syn: scapegrace,
         black sheep]