Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
dŭcēna, ae, f. [duceni], the office of a ducenarius, Cod. Th. 12, 1, 5.
dŭcēni, ae, a (gen. ducenūm, Sen. N. Q. 3, 7, 3; Liv. 7, 25; Plin. 9, 3, 2, § 4), num. distr., two hundred each, two hundred, Plaut. Ps. 3, 2, 40; Hirt. B. G. 8, 4; Liv. 9, 19; 40, 18; Plin. 7, 2, 2, § 28 et saep.