The Collaborative International Dictionary of English v.0.48:

Innermost \In"ner*most`\ ([i^]n"n[~e]r*m[=o]st`), a. [A
   corruption of inmost due to influence of inner. See
   Inmost.]
   Farthest inward; most remote from the outward part; inmost;
   deepest within. --Prov. xviii. 8.
   [1913 Webster]

WordNet (r) 3.0 (2006):

innermost
    adj 1: being deepest within the self; "one's innermost feelings"
           [syn: inmost, innermost]
    2: situated or occurring farthest within; "the innermost
       chamber" [syn: inmost, innermost]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "innermost":
   anonymous, central, closet, deep, incognito, indoor, inmost, inner,
   inside, interior, internal, intestine, intimate, intrinsic, inward,
   isolated, personal, private, privy, retired, secluded, sequestered,
   withdrawn