Jellied fish is a traditional dish made from fish that has been cooked and then jellied with gelatin or other thickening agents. It is usually served cold and is popular in many cultures, including Eastern European and Scandinavian countries. The term 'jellied fish' can also refer to EEL, which is a type of fish that is often used in this dish. EEL is a three-letter word, making it the solution to this crossword puzzle.