Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Mĕtăpīnus, a, um [etym. dub.], Metapinic, an epithet of the second or middle of the three principal mouths of the Rhone: cujus ora appellata … alterum Metapinum, Mart. Cap. 6, § 635; Plin. 3, 4, 5, § 32.