Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
mulctrum, i, n. [mulgeo], a milking-pail: illic injussae veniunt ad mulctra capellae, Hor. Epod. 16, 49; Val. Fl. 6, 145; Calp. Ecl. 3, 66; 4, 25; 5, 33; 9, 36; Prud. Cath. 3, 66: mea, Nemes. Ecl. 2, 35; cf. mulctra.