Katy, bar the door
The expression Katy, bar the door means to watch out or serves as a warning of impending disaster. It dates to at least 1902 when it appears in Hugh McHugh’s (George V. Hobart’s) It’s Up to You:
It was “Katie, bar the door” with her.
But who was Katy (or Katie) and why was she locking the door?
Copyright 1997-2016, by David Wilton