Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
dīlūcŭlum, i, n. [diluceo], daybreak, dawn (cf. crepusculum), Plaut. Am. 2, 2, 105; Cic. Rosc. Am. 7, 19; id. Att. 16, 13, a; cf. Macr. S. 1, 3 fin.; Censor. 24; Vulg. Luc. 24, 1 et saep.
In plur., Fronto, Ep. ad Anton. 1, 5.