The term 'BACK IN' can be solved by three different crossword solutions: RETRO (5 letters), STERN (5 letters), and RETR (4 letters). RETRO is a term used to describe something that is out of fashion but is now making a comeback. It is often used to describe styles from the past that are becoming popular again. STERN is an adjective meaning serious, strict, or severe. RETR is a shortened version of the word retrograde, which means to move backward or return to an earlier state.