Source : Webster's Revised Unabridged Dictionary (1913)

Innermost \In"ner*most`\, 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.

Source : WordNet®

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