Definitions of cinch:

• noun:   a form of all fours in which the players bid for the privilege of naming trumps
• noun:   any undertaking that is easy to do
• noun:   stable gear consisting of a band around a horse's belly that holds the saddle in place
• verb:   get a grip on; get mastery of
• verb:   make sure of
• verb:   tie a cinch around

  Example: "Cinch horses"