Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† hĕlēŏsĕlīnon or hĕlīŏsĕlīnum, i, n., = ἑλειοσέλινον, smallage, celery, Apium graveolens, Linn.; Plin. 19, 8, 37, § 124; 20, 11, 46, § 117; Pall. Apr. 3.