Slumber/ˈslʌmbər/ Definition 1 of 3Pro Tip 1/2Depth Variation Describes the quality of sleep; 'deep slumber' indicates very sound sleep. Exhausted from the hike, she drifted into a deep slumber. Pro Tip 2/2Peaceful Imagery 'Peaceful slumber' can evoke a tranquil and serene sleeping scene. The baby's peaceful slumber was a relief to the parents.