Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sēmĭ-rŏtundus, a, um, adj., half-round, semicircular (Appuleian): subterraneum, App. M. 11, p. 260, 2: suggestus, id. ib. 5, p. 160, 2.