underwater vs subaqueous

underwater and subaqueous both are adjectives.

Word	Noun	Adjective	Verb	Adverb
underwater	No	Yes	No	No
subaqueous	No	Yes	No	No

As adjectives, underwater and subaqueous are synonyms defined as:

Other synonyms of underwater include subaquatic, submerged, submersed.

underwater (adjective)	subaqueous (adjective)
growing or remaining under water	growing or remaining under water
beneath the surface of the water