Dismal is a dreary, depressing sort of bad. "With the cold rain and their team behind by six field goals, the mood in the stands was so dismal even the cheerleaders had lost their 'Rah.'"
Dismal comes from the Latin dies mali which means "bad days." There is a hopelessness implied in the word. If you fell on the way to school and cut your knee, it would be bad, but not dismal. If you fell into a giant mud puddle and had to wear dirty, crusty clothes until you got home, it might make the school day seem pretty dismal.
