Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sēmustŭlo (sēmĭ-ustŭlo, -tĭlo, v. Beier ad Cic. Tull. p. 33, a.; Cod. Erf. has semiustilo, Cic. Mil. 13, 33), no perf., ātum, 1, v. a. (only in part. perf. and fut.), to half burn, to burn in part: infelicissimis lignis semustulatus, Cic. Mil. 13, 33: faces mcendisti, quibus semustulatus ille est, id. Phil 2, 36, 91: semustulatus effugit, id. Tull. 18, 33; Varr. ap. Non. 263, 21: pauci semustulati venere in potestatem, Curt. 6, 6, 32: corpus in amphitheatro semustulandum, Suet. Tib. 75 fin.; cf. semustus.