innermost

Etymology

From Middle English innermost, innermest, in-nermast, alteration (due to Middle English inner, innere (“inner”)) of Old English innemest (“innermost”), equivalent to inner + -most.

adj

1. Farthest inside or towards the center or middle.
   She poured her innermost feelings into her journal.
   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. 2013-06-14, Jonathan Freedland, “Obama's once hip brand is now tainted”, in The Guardian Weekly, volume 189, number 1, page 18

noun

1. That which is innermost; the core.
   […] 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. 1977, Michael Spence Lowdell Morris, The Spirit of Michael Webfoot, page 10