Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
trĭfurcus, a, um, adj. [ter-furca], having three forks, prongs, or points, threeforked, three-pronged: surculi, Col. 5, 11, 7: stirps, id. 5, 10, 7: semina, id. Arb. 20, 2.