happy day—the day of marriage ceremony:
- “When’s the happy day?” Cubitt said and they all smiled.
happy days—is used as a toast:
- “Happy days!” cried Mobbs. “Cheers!” said the Major gloomily.
Note: The expression does not correlate in meaning with the phrase heavenly days—(exclam.) used to express amazement and disbelief with negative coloring:
- Heavenly days! Look what happened. The dog did it again on the Persian carpet!