Theater and theatre are variation on spelling, and both originally referred to the stage theatre. 

 

Movie is a term that was derived from “moving pictures,” as originally movies were a series of still photographs shown in succession to simulate movement (35mm film and even digital are comprised of series of still images, but in much more rapid succession than the first movies). Movie house is simply the place one goes to watch movies.

 

Film is derived from the photographic and later 35mm film that is used to capture the images to create movies. Film house is of course the location of viewing films. 

 

The big screen comes from the comparison of the movie theatre screen to the television screen, the movie theatre being big and the TV being small. 

 

The flea pit comes from the UK, and refers to either the fact that the movie theatres were considered seedy places where the seats were infested with fleas, or from the idea that people looked like they were being bit by fleas because the uncomfortable seats made them fidget.