pressmark vs call number

pressmark and call number both are nouns.

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

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

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

Other synonyms of pressmark include call mark.

pressmark (noun)	call number (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