Noun
(philosophy) A property that applies to all members of a species and only to them, serving to distinguish the species from other species within the same genus, yet is not part of the true definition or the essence of the species.
(theology) selfhood
Source: en.wiktionary.orgCelebration Before 1910 the difficulty of harmonizing the Proprium de Tempore and the Proprium Sanctorum, to which reference has been made, was only partly met in the thirty-seven chapters of general rubrics. Source: Internet
The Proprium Sanctorum This contains the lessons, psalms and liturgical formularies for saints' festivals, and depends on the days of the secular month. Source: Internet