Is stagecoach a common or proper noun?

The noun 'stagecoach' is a common noun, a general Word for any large horse-drawn vehicle formerly used to carry passengers and often mail along a regular route between two places.

A proper noun is the name of a specific person, place, thing, or a title, such as The Stagecoach Tavern in Sheffield MA, or the John Wayne movie 'Stagecoach'.