Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sorbum, i, n. [sorbus], the fruit of the sorbus, a sorb-apple, sorb, service-berry, Plin. 15, 21, 23, § 85; Cato, R. R. 7, 5; Varr. R. R. 1, 59, 3; Col. 12, 16, 4; Verg. G. 3, 380.
sorbus, i, f., the true sorb- or servicetree: Sorbus domestica, Linn.; Col. 5, 10, 19; Plin. 16, 18, 30, § 74; Pall. Jan. 15, 1 al.