Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
crustŭlum, i, n. dim. [crustum], small pastry, confectionery, Varr. L. L. 5, § 107 Müll.; Hor. S. 1, 1, 25; 2, 4, 47; Juv. 9, 5; Sen. Ep. 99, 27; Inscr. Grut. 100, 5 al.