hat (n.) Look up hat at Dictionary.com
Old English hæt "hat, head covering" (variously glossing Latin pileus, galerus, mitra, tiara), from Proto-Germanic *hattuz "hood, cowl" (cognates: Frisian hat, Old Norse hattr, höttr "a hood or cowl"), from PIE root *kadh- "cover, protect" (cognates: Lithuanian kudas "tuft or crest of a bird," Latin cassis "helmet"). To throw one's hat in the ring was originally (1847) to take up a challenge in prize-fighting. To eat one's hat (1770), expressing what one will do if something he considers a sure thing turns out not to be, is said to have been originally eat Old Rowley's [Charles II's] hat.