- 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)
- unexpected, unforeseen - happening or coming quickly and without warning; "a sudden unexpected development"
Antonym: gradual (indirect, via sudden)