The word comes from an unseen character in the play Speed the Plow, a 5-act comedy, written by Thomas Morton in 1798.
She was a prudish character that is referred to, but never appears on the scene. The word Grundyism, to describe this behavior, came into use in Britain in the 1830s. The line “What would Mrs. Grundy say?” became commonplace. Mrs. Grundy became a symbol of conventional morality.
If you have never heard of Thomas Morton, it isn’t surprising. He fell into obscurity and is now known primarily because of the character of Mrs. Grundy. In the very first scene of the play, she is mentioned by Dame Ashfield, and it is through Dame Ashfield that we learn of Mrs. Grundy’s disapproving nature.
Wikipedia reports that there was a real Mrs. Grundy, the head housekeeper at Hampton Court during the reign of Queen Victoria.
An Australian newspaper, quoting Ernest Law, historian of Hampton Court, reveals that this Mrs. Grundy was a sort of moral regulator. She impounded artwork that she considered unsuitable for public display in one of the dark “mystery” chambers of the palace, and kept them under lock and key, in defiance of orders from the Queen’s surveyor of pictures. This room is still referred to as “Mrs. Grundy’s Gallery” and its door is rarely opened.
The term grundyism is still used today in Britain and other countries of Europe to describe people who spend time disapproving of the morality of others. I’ve never heard it used this side of the Atlantic!
However, there was a character in the Archie comics called Miss Grundy, who was named after the original Mrs. Grundy of the play Speed the Plow. She was a teacher who pushed her students hard (especially Archie!), but really cared about them. About five years ago, she was “killed off”, supposedly dying from kidney failure.
Science fiction author Robert Heinlein had this to say about Grundyism: