gear wheel vs cog

gear wheel and cog both are nouns.

Word	Noun	Adjective	Verb	Adverb
gear wheel	Yes	No	No	No
cog	Yes	No	Yes	No

gear wheel (noun)	cog (noun)
a toothed wheel that engages another toothed mechanism in order to change the speed or direction of transmitted motion	tooth on the rim of gear wheel
	a subordinate who performs an important but routine function

gear wheel (verb)	cog (verb)
	join pieces of wood with cogs
	roll steel ingots