For what purpose or reason, why, as in I know you're going to England, but what for? [Mid-1700s]
A punishment or scolding, as in You'll get what for from Mom if she catches you smoking, or The teacher really gave Bud what for. [Colloquial; second half of 1800s]
Dictionary.com presents 366 FAQs, incorporating some of the frequently asked questions from the past with newer queries.