形容说话轻率，说错了随口更正。古时写字用黄纸，写错了就用雌黄涂抹后重写to make rash statements and correct them on the spot; to have a mouth full of orpiment; in Imperial China, the yellow pigment orpiment was used to alter mistakes made when writing on the yellow paper used at the time

• 王衍如果觉得义理有所不安的话,随即就会改口陈说新义,世人谓之“口中雌黄”。"

  If Wang Yan felt uncomfortable about any part of his argument, he would alter it on the spot and set out a new one. People said that he had a "mouth full of orpiment".