clerk vs postal clerk

clerk and postal clerk both are nouns.

Word	Noun	Adjective	Verb	Adverb
clerk	Yes	No	Yes	No
postal clerk	Yes	No	No	No

As nouns, postal clerk is a hyponym of clerk; that is, postal clerk is a word with a more specific, narrower meaning than clerk:

clerk: an employee who performs clerical work (e.g., keeps records or accounts)
postal clerk: a clerk in a post office

clerk (noun)	postal clerk (noun)
an employee who performs clerical work (e.g., keeps records or accounts)	a clerk in a post office
a salesperson in a store

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