Impiously tells you HOW someone acted: in a way that shows a lack of respect for religion or for God. He spoke impiously; she laughed impiously during the prayer. Like impious, it is formal and a little old-fashioned. It does not mean “very badly” in a general sense, and it does not mean “naughtily” in the warm, teasing sense. It points at the sacred thing that was treated lightly. In everyday talk, people more often say disrespectfully, or they name the act: she joked about the temple. Use this adverb when the manner itself is the religious slight.