A set of four works of art that are connected, and that can be seen either as a single work or as four individual works. They are commonly found in literature, film, or video games.

plural of tetralogy

(medicine) A congenital heart defect, characterised by the four findings of ventricular septal defect, pulmonary stenosis, right ventricular hypertrophy and an overriding aorta.

plural of tetralogy of Fallot