call number vs pressmark

call number and pressmark both are nouns.

Word	Noun	Adjective	Verb	Adverb
call number	Yes	No	No	No
pressmark	Yes	No	No	No

As nouns, call number and pressmark are synonyms defined as:

call number and pressmark: a mark consisting of characters written on a book; used to indicate shelf location

Other synonyms of call number include call mark.

call number (noun)	pressmark (noun)
a mark consisting of characters written on a book; used to indicate shelf location	a mark consisting of characters written on a book; used to indicate shelf location