piston ring vs plunger

piston ring and plunger both are nouns.

Word	Noun	Adjective	Verb	Adverb
piston ring	Yes	No	No	No
plunger	Yes	No	No	No

piston ring (noun)	plunger (noun)
seal consisting of a split metal ring that seals the gap between a piston and the cylinder wall	mechanical device that has a plunging or thrusting motion
	hand tool consisting of a stick with a rubber suction cup at one end; used to clean clogged drains
	someone who risks losses for the possibility of considerable gains
	someone who dives (into water)