first of the ten Heavenly Stems 十天干[shi2 tian1 gan1]; (used for an uns
Origin unclear. Possibly depicts cracks on a shell or tree bark.
《說文》：“甲，東方之孟，陽气萌動。从木戴孚甲之象。一曰人頭宜為甲，甲象人頭。，古文甲，始於十，見於千，成於木之象。”