inmost
From Longman Dictionary of Contemporary Englishinmostin‧most /ˈɪnməʊst $ -moʊst/ adjective [only before noun] 1 PRIVATE/PERSONALyour inmost feelings, desires etc are your most personal and secret ones In his inmost heart, he knew he didn’t love me.2 formalIN/INSIDE furthest inside a place, and so difficult to see or find Apparently there are bats in the inmost caves.