The Collaborative International Dictionary of English v.0.48:

Thorow \Thor"ow\, prep.
   Through. [Obs.] "Thorow bramble, pits, and floods." --Beau. &
   Fl.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Thorow \Thor"ow\, a.
   Thorough. [Obs.] --Hakluyt.
   [1913 Webster] Thorp