Something made up of a number of parts that are held or put together in a particular way: hierarchical social structure. The way in which parts are arranged or put together to form a whole; makeup: triangular in structure. The interrelation or arrangement of parts in a complex entity: political structure; plot structure. Something constructed, such as a building. Biology The arrangement or formation of the tissues, organs, or other parts of an organism. Biology An organ or other part of an organism. To give form or arrangement to: structure a curriculum; structure one's day.