Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† Arctŏphylax, ăcis, m., = Ἀρκτοφύλαξ, the Bear-keeper, a constellation, usu. called Bootes, Cic. Arat. Phaen. 394 B. and K.; id. N. D. 2, 42, 109 (as transl. from Arat. 92); so Luc. 8, 180.