Oat Opera Meaning

(idiomatic) A, film, or novel depicting adventures of characters in the American Old West; a western.

Example: 1989, The Time Out Film Guide (retrieved 21 Nov. 2012):
  A queasy combination of classic Wayne oat opera and happy jalopy jokiness a la Butch Cassidy and the Sundance Kid.
1949, "Shows Rank High, But Net Lacks Control," The Billboard, 12 Feb. (retrieved 21 Nov. 2012):
  The fourth of the shows directly under the NBC wing is the Hopalong Cassidy oat opera film series (see box on this page).
1961, National 4-H Club News. (retrieved 21 Nov. 2012):
  WITH THE THUNDER of boots setting the stage, a group of hard-riding horsemen burses into view. This is not a new oat opera on TV, but a group which combines love of 4-H with love of horses--the Perry County Boots and Saddle 4-H Club.