fourth, cube

丁 depicts the thick stem of a plant, which can also be used as a nail or wedge, so 丁 also means nail. However, the meaning of nail is then replaced by 釘, now 丁 is only used to describe a strong man. On the other hand, 丁 is also used as the forth of TianGan since 丁 is the forth stage of the plant's growth. On the other, since a nail is small, 丁 is also used to describe something small.