roman type vs proportional font

roman type and proportional font both are nouns.

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

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

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

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