The Collaborative International Dictionary of English v.0.48:

Cinch \Cinch\, v. t. [imp. & p. p. Cinched; p. pr. & vb. n.
   Cinch"ing.]
   1. To put a cinch upon; to girth tightly. [Western U. S.]
      [Webster 1913 Suppl.]

   2. To get a sure hold upon; to get into a tight place, as for
      forcing submission. [Slang, U. S.]
      [Webster 1913 Suppl.]