The Collaborative International Dictionary of English v.0.48:

Overstep \O`ver*step"\, v. t. [imp. & p. p. Overstepped; p.
   pr. & vb. n. Overstepping.] [AS. ofersteppan.]
   To step over or beyond; to transgress; as, to overstep the
   bounds of propriety. --Shak.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

overstep
    v 1: pass beyond (limits or boundaries) [syn: transgress,
         trespass, overstep]
    2: be superior or better than some standard; "She exceeded our
       expectations"; "She topped her performance of last year"
       [syn: exceed, transcend, overstep, pass, go past,
       top]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "overstep":
   abuse a privilege, advance upon, bother, break bounds, encroach,
   encroach upon, exaggerate, exceed, go beyond, go too far,
   impose on, impose upon, inconvenience, infringe, intrude, invade,
   irrupt, know no bounds, make an inroad, make free with,
   obtrude upon, outstep, overdo, overgo, overjump, overleap,
   overpass, overreach, overrun, overshoot, overshoot the field,
   overshoot the mark, overstep the bounds, overstride, pass,
   presume on, presume upon, superabound, surpass, take a liberty,
   take liberties, transcend, transgress, trespass, trouble, usurp