Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Cassĭtĕrĭdes, um, f., = Κασσιτερίδες, the tin-islands, Cassiterides, now prob. the Scilly Islands, Mel. 3, 6, 2; Plin. 4, 22, 36, § 119; named from the tin found there; v. cassiterum.