Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
admĭnistrātōrĭus, a, um, adj. [administrator], performing the duties of an assistant, helper; serving, ministering: angeli, qui sunt administratorii spiritus, Hier. ad Jes. 46, 11; cf. Vulg. Hebr. 1, 14.