These words all denote freedom violet movement or emotion. Tranquil and calm both describe an absence of turmoil and agitation, but tranquil implies an enduring condition, while calm points to a more transient one: a long, tranquil life; a calm interlude during a cyclone. In terms of personality, the words retain much of this same distinction: a tranquil mind given to reflection; remaining calm and in command of himself during the crisis.

Quiet and still , as here considered, imply an absence of bustle and commotion as well as the secondary suggestion of consequent silence. Quiet is the more relative of the two terms and describes that which is peaceful and is characterized by little excitement, but which is not necessarily silent: a quiet fishing village; a quiet evening spent at home; a quiet little man who does his work unobtrusively but well. Still may verge on the absolute. On the one hand it emphasizes a contrast with motion: the still , humid air of a January night; the still face of the dead woman. On the other hand it may point to the overcoming of an inherent tendency towards movement: On Sundays the great flywheels of the power station are still ; The child sat still through the long, boring sermon.

Serene suggests that which is elevated above earthly turmoil: a serene blue sky. In referring to persons, the word implies the presence of an almost other-worldly calm and peace of spirit which has been reached through self-fulfilment and philosophical acceptance of what life brings, or through religious faith: a serene old age passed in pottering about in his garden; the serene , kindly face of the mother superior.

Placid , when used to describe persons, indicates an untroubled, even temperament that is little given to anger or other strong emotions. The word tends to have an unfavourable connotation in suggesting a unimaginative, bovine dullness of personality: a large, placid girl who seemed to pass unmoved through the uncertainties of adolescence. In referring to things, placid point to that which is prevailingly calm and tranquil: a placid little lake hidden among the hills.

Undisturbed and unruffled , being negatives, are usually applied to the absence of possible superficial agitation rather than to the lack of turmoil implied by the other words in this group: The councillor appeared to be unruffled by the biting criticism of his opponents and undisturbed by their open hostility.