— out of the blue
— surprising
— unaccepted
— unannounced
— unanticipated
— uncivilised
— uncivilized
— uncooperative
— uncouple
— uncover
— uncovered
— unexpectedly
— unexpressed
— unexpressive
— unforeseen
— unheralded
— unhoped
— unhoped-for
— unlooked-for
— unmixable
— unoccupied
— unpredicted
— unprovided for
— unsafe
— unsparing
— unspeakable
— unspecific
— unspecified
— unspoiled
— unspoken
— unthought
— unthought-of
— unusable
— upset