The Collaborative International Dictionary of English v.0.48:

Quietude \Qui"e*tude\, n. [L. quietudo: cf. F. qui['e]tude.]
   Rest; repose; quiet; tranquillity. --Shelley.
   [1913 Webster]

WordNet (r) 3.0 (2006):

quietude
    n 1: a state of peace and quiet [syn: tranquillity,
         tranquility, quietness, quietude]