Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
tĕgillum, i, n. dim. [tegulum], a small covering, a hood or cowl, Plaut. Rud. 2, 7, 18; Varr. ap. Non. 179, 4; cf.: tegillum cuculiunculum ex scirpo factum, Fest. p. 366 Müll.