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]