Dysfunction, difficult, abnormal
Dys- comes from Greek "dys-" (bad, difficult, abnormal) and signals that something functions badly, with difficulty, or abnormally: dyslexia = difficulty reading (not a lack of intelligence, but a different processing style); dysfunction = abnormal or impaired functioning; dystopia = a society that functions in a perverse or dysfunctional way (the opposite of utopia); dysphagia = difficulty swallowing. It is the direct opposite of eu- (good, normal).