influenza
n.a common illness that causes a fever, body aches, and a cough. It is more serious than a cold and is often called the flu.
n.an acute, highly contagious viral infection of the respiratory tract, typically characterised by inflammation of the mucous membranes, fever, and muscular pain.
“He stayed home from work because he had influenza.”
“Health officials recommend getting a vaccine every year to protect against the most common strains of influenza.”
“The 1918 influenza pandemic remains one of the deadliest events in human history, illustrating how rapidly a respiratory virus can spread across a globally connected population.”
Often used with the definite article ('the flu') in common speech; 'influenza' is preferred in medical or formal contexts.
When using the full medical term, it is treated as an uncountable mass noun and does not take an indefinite article.
From Italian influenza (“influence”), from Latin influentia. Doublet of influence.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.