pencil pusher vs clerk

pencil pusher and clerk both are nouns.

Word	Noun	Adjective	Verb	Adverb
pencil pusher	Yes	No	No	No
clerk	Yes	No	Yes	No

As nouns, clerk is a hypernym of pencil pusher; that is, clerk is a word with a broader meaning than pencil pusher:

pencil pusher: a clerk who does boring paperwork
clerk: an employee who performs clerical work (e.g., keeps records or accounts)

pencil pusher (noun)	clerk (noun)
a clerk who does boring paperwork	an employee who performs clerical work (e.g., keeps records or accounts)
	a salesperson in a store

pencil pusher (verb)	clerk (verb)
	work as a clerk, as in the legal business