Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
bĭmātris, e, adj. [bis-mater], having two mothers, poet. epithet of Bacchus (v. Bacchus init.): satumque iterum solumque bimatrem, Ov. M. 4, 12; Hyg. Fab. 167; Anthol. Lat. 1, 19, 2 (where it is scanned bīmăter).