The Collaborative International Dictionary of English v.0.48:

Conventionality \Con*ven`tion*al"i*ty\, n.; pl.
   Conventionalities.
   The state of being conventional; adherence to social
   formalities or usages; that which is established by
   conventional use; one of the customary usages of social life.
   [1913 Webster]

WordNet (r) 3.0 (2006):

conventionality
    n 1: conformity with conventional thought and behavior
    2: unoriginality as a result of being too conventional [ant:
       unconventionality]
    3: orthodoxy as a consequence of being conventional [syn:
       conventionality, convention, conventionalism] [ant:
       unconventionality]