Proper which also had recent use as a slang interjection conveying approval, is given definitions in M-W as noun, adjective, and adverb. A use I think of as common (virtuous) is described as archaic. The noun form is defined as 1 : the parts of the Mass that vary according to the liturgical calendar 2 : the part of a missal or breviary containing the proper of the Mass and the offices proper to the holy days of the liturgical year. The abverb form is a stretch, defined as (chiefly dialect) : in a thorough manner : COMPLETELY.

Mean is a verb (he means to win) or an adjective (that mean old lady next door), and in mathematics it is a noun.