1.  n. a very square person.  This nerd was the most unbelievable cube you have ever seen.  
2.  n. a die, one of a pair of dice. (Usually in the plural.)  She shook the cubes, saying, “Baby needs shoes!”  
3.  n. a sugar cube impregnated with LSD. (Drugs. Often in the plural.)  First they took it on cubes. Then on little bits of paper.