adj. 1 a of, holding, or concerning property (the proprietary classes). b of or relating to a proprietor (proprietary rights). 2 held in private ownership. proprietary medicine any of several drugs, medicines, etc. produced by private companies under brand names. proprietary name (or term) a name of a product etc. registered by its owner as a trade mark and not usable by another without permission.
[ LL proprietarius (as PROPERTY) ]