To bedeck something is to decorate it by hanging or spreading things all over it — flags along a street, flowers through a hall, lights across a building — until the thing is covered. One picture on a wall is not enough; the point is the covering. The word feels a little literary. In speech people more often say decorate, dress, or deck out. It is the old prefix be- (do this thoroughly to something) plus deck, the same deck as in “deck the halls.” Sister verbs in Dutch and German still mean “to cover,” which is the older idea: you overlay a thing with ornaments. There is even a rare English twin, bethatch, from the same covering sense. Though actually, do not picture a ship’s deck when you hear this verb; that is another use of deck.