Lewis & Short

Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.

Messāpĭa (Mesāpĭa), ae, f., the old name of a part of Lower Italy (Apulia and Calabria): Messapia Apulia a Messapo rege appellata, Paul. ex Fest. p. 125 Müll.; cf. Plin. 3, 11, 16, § 99.
Hence, Messāpĭus (Mesāp-), a, um, adj., of or belonging to Messapia, Messapian, Apulian, Calabrian: arva, Ov. M. 14, 513.
In plur., as subst.: Messāpii (Mesāp-), ōrum, m., the Messapians, Liv. 8, 24.