What is a pun?
At its most basic, a pun is a way of using the sound of words to make a connection between meanings that don’t exist otherwise. The husband confuses impotent for important. Of course, the major point of the joke is the ridiculous spectacle the man makes of himself because of his mistake. A minor point is the slim connection between his biological impotence and his impotence in language, although you can laugh at the pun without explicitly making that connection.
