Morphological operators have been ued extensively for description of shapes of binary objects. Often it involves ''probing'' the object with different structuring elements and establishing a degree of similarity with each of these. The skeleton of an image has been used as an effective shape descriptor. In this paper an ''absolutely disjoint skeleton'' has been defined. Decomposition of an image in terms of such a skeleton allows us to define a ''skeleton spectrum''. Finally a shape descriptor has been devised which allows to rank similarity in shape of a given image with respect to a set of structuring elements. Results have been presented for two sample images.