Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Perseus.
†† ăros, i, f., also ăron or ărum, i, n., = ἄρον, wake-robin: Arum dracunculus Linn.: quod aron vocant, Plin. 19, 5, 30, § 96; and id. 24, 16, 91, § 142.
ărum, i, v. aros.