oater in American English
(ˈoutər) noun. slang. a movie, television show, etc., about the frontier days of the U.S. West; western; horse opera.
Why is a Western flick called an oater?
oat·er. A movie about frontier or cowboy life; a western. [From the prominence of horses, known for their taste for oats, in such films.]
What is a Oater film?
A horse opera, hoss opera, oat opera or oater is a Western movie or television series that is clichéd or formulaic, in the manner of a soap opera.