ill / sick Sick is the less formal word, and it usually describes a more temporary health
problem – often nausea, although not always.
If you’re feeling sick, you might need to vomit.
If you get the flu, you might be sick for two weeks.
If a child is sick, he stays home from school that day.
Taking a day off from work for health reasons is called “taking a sick day.”
Ill is the more formal word, and it usually describes a more serious, more
permanent health problem, like cancer.