noun, na-adjective
A feeling or state of uncertainty about the truth, correctness, or appropriateness of something. Used both as a noun and as a na-adjective (疑問な, 疑問に思う).
彼の説明には疑問が残る。
His explanation leaves some questions unanswered.
その計
I felt doubtful about the plan.
彼女の行動は疑問だ。
Her behavior is questionable.