|an arrangement of five objects, as trees, in a square or rectangle, one at each corner and one in the middle.|
|an extraordinary or unusual thing, person, or event; an exceptional example or instance.|
antigen an·ti·gen (ān'tĭ-jən)
Any of various substances, including toxins, bacteria, and the cells of transplanted organs, that when introduced into the body stimulate the production of antibodies. Also called allergen, immunogen.