Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
succinctōrĭum, ii, n. [succingo], an apron (late Lat.), Aug. Gen. adv. Manich. 2. 15 fin.; id. Serm. Verb. Dom. 10 fin.; id. Civ. Dei, 14, 17 al.