innermost

inner +‎ -most.

• (General American) IPA^(key): /ˈɪnɚmoʊst/

innermost (not comparable)

1. Farthest inside or towards the center or middle.
   • 2013 June 14, Jonathan Freedland, “Obama's once hip brand is now tainted”, in The Guardian Weekly, volume 189, number 1, page 18:

     Now we are liberal with our innermost secrets, spraying them into the public ether with a generosity our forebears could not have imagined. Where we once sent love letters in a sealed envelope, or stuck photographs of our children in a family album, now such private material is despatched to servers and clouds operated by people we don't know and will never meet.

   She poured her innermost feelings into her journal.

• outermost

innermost (plural innermosts)

1. That which is innermost; the core.
   • 1977, Michael Spence Lowdell Morris, The Spirit of Michael Webfoot (page 10)

     […] he had decided to not seek outside of himself where companionship and friendliness might be a soothing submergence. It seemed he had instead chosen to turn deeply inwards, towards the measures and pains of his wracked innermosts.