Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Mĕnăpĭi, ōrum, m. plur. (Mĕnapis for Menapiis, Mart. 13, 54), a people of Belgic Gaul, between the Meuse and the Scheldt, Caes. B. G. 2, 4, 9; 4, 4, 2; Plin. 4, 17, 31, § 106; Tac. H. 4, 28; Inscr. Orell. 749.
Hence,