Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
saepīmentum (sēp-), i, n. [saepio], a hedge, fence, enclosure, Varr. R. R. 1, 14, 1 sq.; Cic. Leg. 1, 23, 62.
sēpīmen = sēpīmentum, v. saep