Out of the blue – meaning and origin of the English idiom

by Jakub Marian

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Out of the blue is an English idiom meaning “suddenly and unexpectedly”. You can use it when you are surprised by something that was not expected to happen. For example,

I haven’t seen her since childhood. Then, completely out of the blue, I received a letter from her.

How did people come up with such a strange idiom? 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. It is possible to say that something unexpected is a bolt from the blue. While it would make sense that this “bolt” is a projectile fired from a crossbow (these are called “bolts”, not arrows), it is much more likely that it simply refers to a thunderbolt, i.e. lightning accompanied by thunder—who would expect a thunderbolt from a clear blue sky?

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