Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
alterculum or altercum, i, n., henbane: quae (herba) Apollinaris, apud Arabas altercum sive altercangenum, apud Graecos vero hyoscyamus appellatur, Plin. 25, 4, 17, § 35; Scrib. Comp. 181.
Form al-terculum, App. Herb. 4.