In cooking 丁 means small cubes: 鸡丁 (diced chicken), 肉丁 (diced meat). It is also a common surname and the fourth Heavenly Stem.
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An old reading zhēng appears only in the classical reduplication 丁丁, the steady chop-chop sound of an axe felling trees in old poetry. It never appears in modern speech; read dīng everywhere today.
Indexed under the 一 radical, taking the top horizontal as the anchor. One flat stroke crowns the hook below to picture a nail seen from above, the original meaning of 丁 before it picked up the senses 'fourth', 'robust adult', and 'small cube'.
The hook stroke pictures the shaft of the nail descending from the flat head above. With the horizontal cap, the two strokes give the side profile of a driven nail, the pictographic origin of 丁.
