質疑
しつぎ · shitsugi · JLPT N1 · noun
question
質 = substance/quality, 疑 = doubt: a question is a doubt you put into words
質 (shitsu) means quality or substance, and 疑 (gi) means doubt. Together, 質疑 means raising a doubt to be answered, so it is a formal question or challenge rather than a casual one.