Winter ailment is a term used to describe illnesses that are more common during the winter season. These illnesses include the FLU (3 letters), COLD (4 letters), strep (5 letters) and headcold (8 letters). The FLU is an infectious disease caused by the influenza virus, which can cause fever, chills, body aches, fatigue and other symptoms. A COLD is a mild viral infection of the nose, throat and upper airways, which can cause sneezing, sore throat, runny nose and coughing. Strep is a bacterial infection caused by Streptococcus bacteria, which can cause fever, sore throat, swollen lymph nodes and other symptoms. A headcold is a type of COLD that affects the head and sinuses, causing congestion, headache, facial pain and other symptoms.