casing
     n 1: the housing or outer covering of something; "the clock has a
          walnut case" [syn: {shell}, {case}]
     2: the outermost covering of a pneumatic tire
     3: the enclosing frame around a door or window opening; "the
        casings had rotted away and had to be replaced" [syn: {case}]
Source: WordNet® 2.0