Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Sinti or Sintii, ōrum, m., a people of Macedonia: Heraclea ex Sintiis, Liv. 42, 51, 7.
Hence, Sintĭcus, a, um, adj., of or belonging to the Sintii, Sintian: Heraclea Sintica, Plin. 4, 10, 17, § 35; or, Sintice Heraclea, Liv. 45, 29, 6 and 7.