1936, from German Subsidiarität, paraphrasing the Latin of Pius XI in his Quadragesimo Anno of 1931; see subsidiary + -ity.
Entries linking to subsidiarity
subsidiary adj.
1540s, from Latin subsidiarius "belonging to a reserve, of a reserve, reserved; serving to assist or supplement," from subsidium "a help, aid, relief, troops in reserve" (see subsidy). As a noun, c. 1600, "subsidiary thing." In Latin the word was used as a noun meaning "the reserve."
-ity
word-forming element making abstract nouns from adjectives and meaning "condition or quality of being ______," from Middle English -ite, from Old French -ete (Modern French -ité) and directly from Latin -itatem (nominative -itas), suffix denoting state or condition, composed of -i- (from the stem or else a connective) + the common abstract suffix -tas (see -ty (2)).
Roughly, the word in -ity usually means the quality of being what the adjective describes, or concretely an instance of the quality, or collectively all the instances; & the word in -ism means the disposition, or collectively all those who feel it. [Fowler]