This radical was developed from a circle with a central dot as the image of the sun. As you can hardly draw circles or dots with a brush, it became the current rectangular shape.
The character for tall 大 shows a person 人 with outstretched arms 一. If you shift the lower strokes towards each other, you can get the: woman 女. The wider lower area can be understood as female hips?
Tip: Go to the radicals that are contained in this character and learn all the characters with this radical systematically!
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