Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
rētĭārĭus, ii, m. [rete], one who fights with a net, a net-fighter (a kind of gladiator, who endeavored to hold his adversary by throwing a net over his head), Quint. 6, 3, 61; Suet. Calig. 30; id. Claud. 34; Val. Max. 1, 7, 8; Inscr. Orell. 2566; 2578; 4273; cf. Juv. 8, 204 sqq.; v. Dict. of Antiq.; and cf. mirmillo.
Prov.: contra retiarium ferula, to fight with feeble weapons against one well equipped, or, as we might say, to parry a lance with a bodkin, Mart. 2 praef.