Sentence:  Some time in 1912 , Picasso cut out and folded a piece of paper in the shape of a guitar ; to this he glued and fitted other pieces of paper and four taut strings , thus creating a sequence of <WSD>flat</WSD> surfaces in real and sculptural space to which there clung only the vestige of a picture plane . 
Meaning of the word marked with <WSD> tags:  lacking stimulating characteristics; uninteresting