Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
doctor, ōris, m. [doceo], a teacher, instructor, Cic. de Or. 1, 6, 23; 3, 15, 57; id. Div. 1, 3, 6; id. Or. 33, 117; Quint. 2, 2, 2; Hor. C. 4, 6, 25; id. S. 1, 1, 26; Vulg. Matt. 22, 35 et saep.