roman vs proportional font

roman and proportional font both are nouns.

Word	Noun	Adjective	Verb	Adverb
roman	Yes	No	No	No
proportional font	Yes	No	No	No

As nouns, proportional font is a hypernym of roman; that is, proportional font is a word with a broader meaning than roman:

roman: a typeface used in ancient Roman inscriptions
proportional font: any font whose different characters have different widths

roman (noun)	proportional font (noun)
a typeface used in ancient Roman inscriptions	any font whose different characters have different widths