Gilding the lily

The phrase “to gild the lily” means to add unnecessary adornment or supposed improvement: the verb gild means to cover something with a thin layer of gold; and, as a lily is already a beautiful flower, to gild it would be an unnecessary adornment or supposed improvement.  The phrase is a condensation of a line from the Shakespeare play King John: “To gild refined gold, to paint the lily … is wasteful and ridiculous excess.”