Disenchantment is the feeling, or the slow change, of no longer believing that someone or something is as good as you once thought. After the third broken promise, their disenchantment with the club was obvious. It names the cooling itself, not only the person who feels it. Though actually, in university social science the same English word is also used for a bigger idea: Max Weber’s picture of the modern world losing its magic, where people explain things by rules and machines instead of by spirits and wonder. In that specialist sense it is a calque of German Entzauberung. You do not need the classroom sense to use the everyday word; just know that a professor may mean something wider than “I am fed up.”