Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† thapsĭa, ae, f., = θαψία, a poisonous shrub: Thapsia Asclepium, Linn.; Plin. 13, 22, 43, § 124.
Called thapsos, Luc. 9, 919.