Which word would describe an overwhelming sense of calmness and acceptance?

The word "equanimity" refers to a state of mental and emotional stability, especially under tension or stress. It encompasses an overwhelming sense of calmness and acceptance, suggesting that an individual maintains composure and evenness of temper despite adverse circumstances. Equanimity implies not just surface calm but a profound peace of mind and an ability to accept situations as they are without being unduly affected by them.

The other choices, while related to calmness, do not capture the comprehensive nature of the acceptance implied by equanimity. "Dulcet" describes something that is melodious or sweet-sounding, which does not directly relate to emotional states. "Serene" conveys a sense of calm and peacefulness, but does not encompass the same depth of emotional balance and acceptance found in equanimity. "Composed" refers to being in control of oneself and calm in the moment but lacks the connotation of a steady state of mind or acceptance of circumstances that 'equanimity' carries.