Lewis & Short

Pĕlēthrŏnĭus, a, um, adj., of or belonging to a region of Thessaly inhabited by the Lapithœ and Centaurs, Pelethronian: Lapithae, Verg. G. 3, 115: antra, Luc. 6, 386: pinus, a spear cut on the Pelethronian mountains, Stat. Th. 2, 593: Pelethronia cithara, of Achilles (because he, a native of Thessaly, had learned of Chiron the Thessalian to play the cithara), Auct. Priap. 17.
As subst.: pĕlēthrŏnĭa, ae, f., centaury, App. Herb. 34.