clerk vs sorter

clerk and sorter both are nouns.

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

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

clerk: an employee who performs clerical work (e.g., keeps records or accounts)
sorter: a clerk who sorts things (as letters at the post office)

clerk (noun)	sorter (noun)
an employee who performs clerical work (e.g., keeps records or accounts)	a machine for sorting things (such as punched cards or letters) into classes
a salesperson in a store	a clerk who sorts things (as letters at the post office)

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