The Collaborative International Dictionary of English v.0.48:

Extravagancy \Ex*trav"a*gan*cy\, n.; pl. Extravagancies.
   Extravagance.
   [1913 Webster]

WordNet (r) 3.0 (2006):

extravagancy
    n 1: the quality of exceeding the appropriate limits of decorum
         or probability or truth; "we were surprised by the
         extravagance of his description" [syn: extravagance,
         extravagancy]