Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
scămillus, i, m. (acc. to Prisc. p. 615 P., scămellum, i, n.) dim. [scamnum], a little bench or stool: impares, i. e. unequal projections or steps on the pedestals of columns, Vitr. 3, 4, 5; 5, 9, 4; App. 615 P.