Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Prŏcyon, ōnis, m., = Προκύων (Foredog), a constellation that rises before the dog-star (pure Lat. Antecanis), Cic. Arat. 222; Hor. C. 3, 29, 18; Cic. N. D. 2, 44, 144; Col. 11, 2, 52; Manil. 5, 197.