I Ching, Yijing or Zhou Yi
"Oracle of the moon": © 2000 LiSe
Tu, the clod of earth is probably an earth altar.
The meaning of a character can change in the course of centuries, but in compounds (several images making up one character) or words (which are usually a combination of two characters) the old meaning is often retained. Looking at several of those gives a "theme", a basic or comprehensive meaning. (In parenthesis are the meanings of the parts).
The characters (compounds) or words with KUN:
1 (earth axis) axis of earth
2 (earth bag) woman's bag/purse
3 (earth actor) female actor
4 (twist turn heaven earth) change course of events; retrieve a situation
5 (stream) Mawangdui: CHUAN1, the flow or stream, the female organ.
6 (heaven earth) heaven and earth; the universe
Earth as 'yin' or 'female' makes sense in almost all compounds. The character itself contains shen, spirit, electricity, so something mysterious is part of it. The spirits of the deceased, the inheritance which is part of your soul, mind and body.
Meanings of