Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
assercŭlus, i, m. dim. (assercŭ-lum, i, n., Cato) [asser] a small beam or pole, Cato, R. R. 12; 152; Col. 12, 52, 4; 8, 3, 6.