Sentence:  A borderline schizophrenic young man told me that to him the various theoretical concepts about which he had been expounding , in a most articulate fashion , during session after session with me , were like great <WSD>cubes</WSD> of almost tangibly solid matter up in the air above him ; as he spoke I was reminded of the great bales of cargo which are swung , high in the air , from a docked steamship . 
Meaning of the word marked with <WSD> tags:  a three-dimensional shape with six square or rectangular sides