WordNet (r) 3.0 (2006):
out of the blue adv 1: in a way that was not expected; "her brother showed up at the wedding out of the blue" [syn: unexpectedly, out of the blue] adj 1: 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" [syn: unanticipated, unforeseen, unlooked-for, out of the blue(p)]