Adjective out of the blue has 1 sense
  1. unanticipated, unforeseen, unlooked-for, out of the blue - not anticipated; "unanticipated and disconcerting lines of development"- H.W.Glidden; "unforeseen circumstances"; "a virtue unlooked-for in people so full of energy"; "like a bolt out of the blue"
    Antonym: expected (indirect, via unexpected)
,Adverbial out of the blue has 1 sense
  1. unexpectedly, out of the blue - in a way that was not expected; "her brother showed up at the wedding out of the blue"
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