Definition of out of the blue in English:

out of the blue

(or out of a clear blue sky) informal
Without warning; unexpectedly: she phoned me out of the blue
[with reference to a ‘blue’ (i.e. clear) sky, from which nothing unusual is expected]
More example sentences
  • Rarely does a profit warning come out of the blue like the subsequent share price reaction suggests.
  • Quite frankly, this piece of research is so unexpected, so out of the blue, it beggars belief.
  • This particular warning came out of the blue and there must be a worry that there is yet more to come.
See parent entry: blue

Definition of out of the blue in: