1. [adj]  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"
2. [adj]  happening or coming quickly and without warning; "a sudden unexpected development"

UNFORESEEN is a 10 letter word that starts with U.