SOLEMN

[adjective] - serious and without any amusementa solemn face/voiceThis is a far from solemn book - it is a rich mix of pleasures and information, and is full of surprises.A car arrived with three distinguished, grey-haired men in dark suits, looking solemn.The chant was accompanied by solemn (= serious and carefully produced) ritual gestures.A solemn promise/commitment/undertaking is an agreement which you make in a serious way and expect to fulfil.