The Collaborative International Dictionary of English v.0.48:

Unacceptable \Un`ac*cept"a*ble\, a.
   Not acceptable; not pleasing; not welcome; unpleasant;
   disagreeable; displeasing; offensive. --
   Un`ac*cept"a*ble*ness, n. -- Un`ac*cept"a*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unacceptableness
    n 1: unsatisfactoriness by virtue of not conforming to approved
         standards [syn: unacceptability, unacceptableness]
         [ant: acceptability, acceptableness]