Back in the Day is a phrase used to refer to a time in the past, usually in reference to a simpler or more nostalgic time. The crossword solutions for this phrase are ONCE (4 letters), AGO (3 letters), and THEN (4 letters). ONCE refers to a single occurrence in the past, AGO indicates a period of time that has passed, and THEN is used to refer to a specific point in the past. Together, these words can be used to describe a time in the past, such as 'Back in the Day'.