Characterized by appropriateness or suitability; fitting: the proper knife for cutting bread; not a proper moment for a joke. Called for by rules or conventions; correct: the proper form for a business letter. Strictly following rules or conventions, especially in social behavior; seemly: a proper lady; a proper gentleman. Belonging to one; own: restored to his proper shape by the magician. Characteristically belonging to the being or thing in question; peculiar: an optical effect proper to fluids. Being within the strictly limited sense, as of a term designating something: the town proper, excluding the suburbs. Ecclesiastical For use in the liturgy of a particular feast or season of the year. Mathematics Of or relating to a subset of a given set when the set has at least one element not in the subset. Worthy of the name; true: wanted a proper dinner, not just a snack. Out-and-out; thorough: a proper whipping. Thoroughly: beat the eggs good and proper. Ecclesiastical The parts of the liturgy that vary according to the particular feast or season of the year.