The Collaborative International Dictionary of English v.0.48:

Quiescence \Qui*es"cence\, Quiescency \Qui*es"cen*cy\, n. [L.
   quiescentia, fr. quiescens, p. pr.; cf. F. quiestence. See
   Quiesce.]
   The state or quality of being quiescent. "Quiescence, bodily
   and mental." --H. Spencer.
   [1913 Webster]

         Deeds will be done; -- while be boasts his quiescence.
                                                  --R. Browning.
   [1913 Webster]

WordNet (r) 3.0 (2006):

quiescency
    n 1: a state of quiet (but possibly temporary) inaction; "the
         volcano erupted after centuries of dormancy" [syn:
         dormancy, quiescence, quiescency]
    2: quiet and inactive restfulness [syn: quiescence,
       quiescency, dormancy, sleeping]