The term COMMON CAUSE is composed of four crossword solutions: FLU (3 letters), AIR (3 letters), POLLEN (6 letters), and RAIN (4 letters). All of these terms are related to weather and climate, and can be considered common causes of illness, allergies, and other health issues. FLU is an abbreviation for influenza, a contagious respiratory illness caused by a virus. AIR is the atmosphere that surrounds the Earth, which can contain pollutants and allergens that can cause health problems. POLLEN is a fine powder released by plants that can cause allergic reactions in some people. Finally, RAIN is precipitation that falls from the sky, which can bring pollutants and allergens down to the ground. All of these terms can be considered common causes of health issues.