The Collaborative International Dictionary of English v.0.48:

Inaccessible \In`ac*cess"i*ble\, a. [L. inaccessibilis: cf. F.
   inaccessible. See In- not, and Accessible.]
   Not accessible; not to be reached, obtained, or approached;
   as, an inaccessible rock, fortress, document, prince, etc. --
   In`ac*cess"i*ble*ness, n. -- In`ac*cess"i*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inaccessibly
    adv 1: in an inaccessible manner; "located inaccessibly on the
           top of a mountain"