Out of the blue means completely without warning. Nothing led up to it, and nobody saw it coming.
The blue is the clear sky, and the fuller version is a bolt out of the blue, meaning lightning from a cloudless sky, which is exactly as unexpected as anything can be. It is used most about news, phone calls and offers, and it usually goes at the end of a sentence. The phrase carries no judgement about whether the surprise was good or bad, which is part of its usefulness.
1phraseout of the blueCompletely unexpectedly.
“She rang me out of the blue after fifteen years.”
Short for out of the blue sky, likening an unexpected event to lightning or rain coming suddenly from a cloudless sky.
Etymology from Wiktionary, CC BY-SA
Practised in Idioms, A Man Called Ove
First appears in chapter 6 of A Man Called Ove.
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