opera glasses vs field glasses

opera glasses and field glasses both are nouns.

Word	Noun	Adjective	Verb	Adverb
opera glasses	Yes	No	No	No
field glasses	Yes	No	No	No

As nouns, opera glasses and field glasses are synonyms defined as:

opera glasses and field glasses: (plural) an optical instrument designed for simultaneous use by both eyes

Other synonyms of opera glasses include binoculars.

opera glasses (noun)	field glasses (noun)
(plural) an optical instrument designed for simultaneous use by both eyes	(plural) an optical instrument designed for simultaneous use by both eyes