Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
mandĭbŭla, ae, f., or mandĭbŭ-lum, i, n. [2. mando], a jaw (post-class.), Macr. Somn. Scip. 1, 6, 69: cibaria confecta mandibulis, id. S. 7, 4, 14; Isid. 11, 1, 45.