man, cube, fourth

丁 is a pictograph of a nail, depicted in bronze inscriptions as the top view of a nail head and in small seal script as a side view. A nail is hard and durable, thus extending to mean an adult male. The original meaning of 丁 was later replaced by 釘 (nail). Nowadays, 丁 refers to an adult male, a small square block, and is also used to denote the fourth position in the heavenly stems (天干).