betide \bih-TAHYD\ , verb:

1. To happen to; come to; befall.
2. To happen; come to pass.

“Ill luck betide thee, poor damsel,” said Sancho, “ill luck betide thee!”
— Miguel de Cervantes, Don Quixote

“The girls’ skirts are measured each week with a dressmaker’s rule,” she would say, “to see that they conform to the length prescribed. Woe betide any girl whose skirt does not.”
— Hilary Mantel, An Experiment in Love

via Dictionary.com.