He just smiled noncommittally when asked about his opinion on the proposal.

noncommittally 是由形容词 noncommittal 加上副词后缀 -ly 构成的。noncommittal 由前缀 non-（表示"不"）和 committal（承诺）组成，字面意思是"不表态的"。noncommittally 作为副词，表示"不置可否地""含糊地"，形容不明确表态的态度或行为。