コウ, あな, のり
cavity, hole, slit, very, great, exceedingly
JLPT1 G7 S4 F2052
The relevant seal inscription form is 子 child + a mark# → mother and newborn (just passed through the vagina in being born), connected by the curving and now stretched umbilical cord → *hole* (← vagina). *Confucius* is a borrowed meaning.
[Full Kanji Etymology List]