optical bench vs apparatus

optical bench and apparatus both are nouns.

Word	Noun	Adjective	Verb	Adverb
optical bench	Yes	No	No	No
apparatus	Yes	No	No	No

As nouns, apparatus is a hypernym of optical bench; that is, apparatus is a word with a broader meaning than optical bench:

optical bench: apparatus for observation and measurement of optical phenomena
apparatus: equipment designed to serve a specific function

Other hypernyms of optical bench include setup.

optical bench (noun)	apparatus (noun)
apparatus for observation and measurement of optical phenomena	equipment designed to serve a specific function
	(anatomy) a group of body parts that work together to perform a given function