1with object To restore from a ruffled state; to free from folds, wrinkles, irregularities, etc.; to make still or settled.
2no object To become unruffled; to become, or be made, smooth, regular, or even; to become still or settled.
3with object To make (a person, the emotions, etc.) calm or tranquil; to ease or lighten (a situation).
4no object To become calm or tranquil emotionally; to relax, settle down.
Early 17th century; earliest use found in James Mabbe (d. ?1642), translator. From un- + ruffle.