instantaneous sound pressure vs sound pressure

instantaneous sound pressure and sound pressure both are nouns.

Word	Noun	Adjective	Verb	Adverb
instantaneous sound pressure	Yes	No	No	No
sound pressure	Yes	No	No	No

As nouns, instantaneous sound pressure and sound pressure are synonyms defined as:

instantaneous sound pressure and sound pressure: the difference between the instantaneous pressure at a point in a sound field and the average pressure at that point

instantaneous sound pressure (noun)	sound pressure (noun)
the difference between the instantaneous pressure at a point in a sound field and the average pressure at that point	the difference between the instantaneous pressure at a point in a sound field and the average pressure at that point