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):

unacceptably
    adv 1: to an unacceptable degree; "The percentage of lead in our
           drinking water is unacceptably high" [syn:
           unacceptably, intolerably] [ant: acceptably, so-
           so, tolerably]