Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Hĕlĭcāon, ŏnis, m., = Ἑλικάων, son of Antenor and founder of Patavium (Padua): Helicaonis orae, i. e. Patavian, Mart. 10, 93, 1.
Hence, Hĕlĭcāŏnĭus, a, um, adj.: regio, the same, id. 14, 152, 2.