The Collaborative International Dictionary of English v.0.48:

Abstrusity \Ab*stru"si*ty\ ([a^]b*str[udd]"s[i^]*t[y^]), n.
   Abstruseness; that which is abstruse. [R.] --Sir T. Browne.
   [1913 Webster]

WordNet (r) 3.0 (2006):

abstrusity
    n 1: wisdom that is recondite and abstruse and profound; "the
         anthropologist was impressed by the reconditeness of the
         native proverbs" [syn: reconditeness, abstruseness,
         abstrusity, profoundness, profundity]