This word belongs to the illness in which a person cannot stop themselves eating far too much, then tries to control their weight, often by vomiting. As an adjective it means “of or having that illness”: bulimic behaviour, a bulimic episode. As a noun, a bulimic is a person who has that illness. Though actually, many teachers and doctors now prefer “a person with bulimia,” because the noun can make it sound as if the illness is the whole person. The word is medical, and you will also hear it in news and everyday talk; it is not a joke word.