A: Do you remember Mary?

    B: Yeah. I haven’t seen her since college graduation.

    A: Me too. Then, completely out of the blue, I received an email from her yesterday. She invited me to her wedding to be held in Bali next week!

    Note: This idiom means “suddenly and unexpectedly.” You can use it when you are surprised by something that was not expected to happen. The meaning of the word “blue” is revealed by a longer but much less common version of the idiom: out of a clear blue sky. “The blue” refers to the blueness of the sky. Yet another version of the idiom reveals what comes out of a clear blue sky. Something unexpected can be “a bolt from the blue,” here “bolt” referring to “thunderbolt.” It’s easy to understand: Who would expect a thunderbolt from a clear blue sky?