Of, relating to, having, or characterized by structure: structural simplicity. Affecting structure: structural damage. Used in or necessary to building: structural beams. Concerned with or resulting from political or especially economic structure. Geology Of or relating to the structure of rocks and other aspects of the earth's crust. Biology Of or relating to organic structure; morphological. Relating to or concerned with systematic structure in a particular field of study, such as linguistics or the behavioral sciences. A part of a structure that bears a weight, or the structural piece used for such a part.