Slangy goodbye is a term used to describe informal ways of saying goodbye. The crossword solutions for this term are 'CIAO' (4 letters), 'LATER' (5 letters) and 'Seeya' (5 letters). CIAO is an Italian word that is used as a casual greeting or farewell. LATER is an informal way of saying goodbye, often used when parting with friends. Seeya is another informal way of saying goodbye, usually used when parting with someone you know well.