Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† cypērŏs, i, m. (cypērum, i, n., Varr. R. R. 3, 16, 13), = κύπειρος, a kind of rush, Plin. 21, 18, 70, §§ 117 and 118.