Situated or occurring farthest within: the innermost chamber. (adjective)
Most intimate: one's innermost feelings. (adjective)
The part situated farthest in.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "innermost" in a sentence
"The G3C consisted of six layers of nylon (the innermost was a rubberized bladder)."
"The innermost was a dead rock with no atmosphere, while the next was a dead rock with far too much atmosphere."
"The question concerns the very large — space, galaxies, etc. — but also the very small, namely the innermost structure of matter."