Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Termessus, i, f., = Τερμησσός, a town in Pisidia, now Karabunar Kini, Liv. 38, 15.
Hence, Termessenses, ĭum, m., the inhabitants of Termessus, Liv. l. l.