Definition from Wiktionary, the free dictionary
backstairs (plural only)
- A staircase at the rear of a building or one normally only used by servants and tradesmen.
- An indirect or furtive means of access or intercourse.
1934 March 27, “De Valera Move Hits Dignity Of Governor-General”, Christian Science Monitor:
- The straight-forward course, they say, would be to proclaim outright, instead of trying to bring it in by the backstairs.
- Secret or furtive.