Use of なさい in ごめんなさい


Why is なさい used in ごめんなさい when it is usually used as a command form?




免 is a somewhat old word meaning 'forgiveness'. There is a polite command form
that goes お・ご～なさい, such as in おいでなさい or ご覧なさい. If you apply this to 免, you get
ご免なさい, literally 'please forgive me'. This command form is also seen in
おやすみなさい and おかえりなさい.

