Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† ērĭgĕron, ontis, m., = ἠριγέρωϝ, the plant groundsel, Senecio vulg., Linn.; Plin. 25, 13, 106, § 167 sq.; 22, 25, 64, § 133.