Semantic means related to meaning and phonetic means related to sound, so it's simply a character consisting of one part giving the character its meaning and another part giving it its sound. For example, 米 (rice) + 良 (an adjective to describe good things) = 粮 (food)
In the old times of material scarcity, grain was much valued by Chinese people. It was a celebrating event to have grain and not to starve. As a result, "吃了吗？(chī le mɑ)", which mean "have you eaten", has become an usual greeting when Chinese people meet each other.
In the Oracle Bone Seal, "一"in the middle of "米" represents a container to store rice grains, the top three strokes represent rice grains in the container, and the bottom three strokes represent rice grains dropped out of the container.
"良" is an oracle used to refer to the aroma of food. It also means "good things" today.
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