Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
biblĭŏthēcārĭus, ii, m. [bibliotheca], a librarian (late Lat.), M. Aurel. ap. Fronto Ep. ad M. Caes. 4, 5: bibliothecarius qui codices servat, Gloss. Isid.