rapid eye movement vs REM

rapid eye movement and REM both are nouns.

Word	Noun	Adjective	Verb	Adverb
rapid eye movement	Yes	No	No	No
REM	Yes	No	No	No

As nouns, rapid eye movement and REM are synonyms defined as:

rapid eye movement and REM: a recurring sleep state during which dreaming occurs; a state of rapidly shifting eye movements during sleep

Other synonyms of rapid eye movement include paradoxical sleep, rapid eye movement sleep, REM sleep.

rapid eye movement (noun)	REM (noun)
a recurring sleep state during which dreaming occurs; a state of rapidly shifting eye movements during sleep	a recurring sleep state during which dreaming occurs; a state of rapidly shifting eye movements during sleep