character printer vs character-at-a-time printer

character printer and character-at-a-time printer both are nouns.

Word	Noun	Adjective	Verb	Adverb
character printer	Yes	No	No	No
character-at-a-time printer	Yes	No	No	No

As nouns, character printer and character-at-a-time printer are synonyms defined as:

character printer and character-at-a-time printer: a printer that prints a single character at a time

Other synonyms of character printer include serial printer.

character printer (noun)	character-at-a-time printer (noun)
a printer that prints a single character at a time	a printer that prints a single character at a time