'Placidity' definitions:

Definition of 'placidity'

From: WordNet
noun
A feeling of calmness; a quiet and undisturbed feeling [syn: placidity, placidness]
noun
A disposition free from stress or emotion [syn: repose, quiet, placidity, serenity, tranquillity, tranquility]

Definition of 'Placidity'

From: GCIDE
  • Placidity \Pla*cid"i*ty\, n. [L. placiditas: cf. F. placidit['e].] The quality or state of being placid; calmness; serenity. --Hawthorne. [1913 Webster]