Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
trĭ-sulcus, a, um (form trĭsulcis, e, Fulg. Rusp. Ep. 9), adj. [ter] (having three furrows), three-cleft, three-forked, threepointed; threefold, triple (poet.): lingua (serpentis), Verg. A. 2, 475; Plin. 11, 37, 65, § 171: sermo, of the serpent in Paradise, Prud. Ham. 203: ordine trisulco quatit ora fragor, of the teeth, Val. Fl. 2, 500: fulmen, Varr. ap. Non. 448, 20; cf. Fest. p. 352; also called Jovis telum trisulcum, Ov. Ib. 467: ignes, id. M. 2, 848: Sicilia, Claud. Rapt. Pros. 1, 145: fores, folding in three parts, Varr. ap. Serv. Verg. A. 1, 449: ramus, threeforked, Pall. Mart. 10, 24.