The Collaborative International Dictionary of English v.0.48:

Overthwart \O"ver*thwart"\ ([=o]"v[~e]r*thw[add]rt"), a.
   1. Having a transverse position; placed or situated across;
      hence, opposite. "Our overthwart neighbors." --Dryden.
      [1913 Webster]

   2. Crossing in kind or disposition; perverse; adverse;
      opposing. "Overthwart humor." --Clarendon.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Overthwart \O"ver*thwart"\, adv.
   Across; crosswise; transversely. "Y'clenched overthwart and
   endelong." --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Overthwart \O"ver*thwart"\, prep.
   Across; from alde to side of. "Huge trees overthwart one
   another." --Milton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Overthwart \O"ver*thwart`\, n.
   That which is overthwart; an adverse circumstance;
   opposition. [Obs.] --Surrey.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Overthwart \O`ver*thwart"\, v. t.
   To cross; to oppose. [Obs.]
   [1913 Webster]