Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ātrāmentārĭum, ii, n. [atramentum], an inkstand: atramentarium scriptoris, Vulg. Ezech. 9, 2 (as transl. of the Heb. [??]); 9, 3; 9, 11.