1. A series of four related literary (novels), dramatic, artistic, or musical works.
2. A group of four dramas, three tragedies, and one satyr play, performed consecutively at the festival of Dionysus in ancient Athens.
3. Any series or combination of four entities or items.
4. In medicine, the combination of four symptoms or elements.

A congenital heart defect (a structural defect of the heart or great vessels or both that is present at birth, resulting from improper development of the heart and blood vessels during the prenatal period) consisting of four structural anomalies:

• Obstruction to pulmonary flow.
• Ventricular septal defect (abnormal opening between the right and left ventricles).
• Dextroposition of the aorta (aortic opening overriding the septum and receiving blood from both ventricles).
• Right ventricular hypertrophy (increase of volume of the myocardium, or the middle and thickest layer of the heart wall, composed of cardiac muscle of the right ventricle).

Infants with this condition are sometimes referred to as blue babies because cyanosis is an outstanding symptom, since the position of the aorta allows poorly oxygenated blood from the systemic circulation to mix with oxygenated blood from the lungs.

Other symptoms include clubbing of the ends of the fingers, hemoptysis, dyspnea on exertion, and a slight delay in growth and development.

The Statesman, or Politikos in Greek and Politicus in Latin, is a four part dialog contained within the work of Plato (a classical Greek philosopher, who, together with his mentor, Socrates, and his student, Aristotle, helped to lay the foundations of Western philosophy).