A small decorative optical instrument having a low magnification and designed for use at the opera or theatre, originally in the form of a short telescope (now historical), and later (usually in plural) in the form of a small pair of (typically non-prismatic) binoculars.
Origin
Mid 18th century. From opera + glass.
Definition of opera glass in US English:
opera glass
noun
A small decorative optical instrument having a low magnification and designed for use at the opera or theatre, originally in the form of a short telescope (now historical), and later (usually in plural) in the form of a small pair of (typically non-prismatic) binoculars.