pain in the head caused by dilation of cerebral arteries or muscle contractions or a reaction to drugs
"After taking too many painkillers, she woke up with a throbbing headache caused by the medication's side effects."
A pain or ache in the head.
"The loud noise gave me a sudden headache that made it hard to concentrate."
In plain English: A headache is a painful feeling of pressure or throbbing inside your head.
"The loud noise behind my ears caused me a terrible headache all morning."
The word headache comes directly from the combination of the words head and ache, which have been joined in English since at least the 14th century. Its meaning has remained consistent throughout its history, referring simply to pain located in one's head.