in·ner / ˈinər/ • adj. 1. situated inside or further in; internal: an inner courtyard the inner thigh. ∎  close to the center: the inner solar system. ∎  close to the center of power: the inner cabinet.2. mental or spiritual: a test of inner strength. ∎  (of thoughts or feelings) private and not expressed or discernible.• n. the inner part of something: using his rock shoes as inners for his double boots. ∎  (in archery and shooting) a division of the target next to the bull’s-eye. ∎  a shot that strikes this.DERIVATIVES: in·ner·ly adv. ( poetic/lit. ).in·ner·ness n. ( poetic/lit. ).

inner OE. inner(r)a, in(n)ra = OHG. innaro, -ero (G. innere), ON. innri, iðri; compar. f. IN1 (adv.); see -ER3.
Hence innermost XV.