hat (n.)
Old English hæt "hat, head covering," from Proto-Germanic *hattuz "hood, cowl" (cognates: Frisian hat, Old Norse hattr), from PIE root *kadh- "cover, protect" (cognates: Lithuanian kudas "tuft or crest of a bird," Latin cassis "helmet"). Now, "head covering with a more or less horizontal brim." To throw one's hat in the ring was originally (1847) to take up a challenge in prize-fighting. To eat one's hat is said to have been originally To eat Old Rowley's [Charles II's] hat.