The Collaborative International Dictionary of English v.0.48:

Overslow \O`ver*slow"\, v. t.
   To render slow; to check; to curb. [Obs.] --Hammond.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Overslow \O"ver*slow"\, a.
   Too slow.
   [1913 Webster]