valve rocker vs rocker arm

valve rocker and rocker arm both are nouns.

Word	Noun	Adjective	Verb	Adverb
valve rocker	Yes	No	No	No
rocker arm	Yes	No	No	No

As nouns, valve rocker and rocker arm are synonyms defined as:

valve rocker and rocker arm: a lever pivoted at the center; used especially to push a valve down in an internal-combustion engine

valve rocker (noun)	rocker arm (noun)
a lever pivoted at the center; used especially to push a valve down in an internal-combustion engine	a lever pivoted at the center; used especially to push a valve down in an internal-combustion engine