It can't be a single word. Noon is the definite word, and sunshine is the noun. In ancient Chinese, there is no single word specifically used to refer to the midday sunshine. For details, see Liezi Tang Wen-Two Children Arguing about the Sun. A son said that "the sun rises as big as a hood, and Japan is like a vegetable vat", which can better illustrate this point. Japan and China are called midday sun (sunshine).
Or you should ask in another way, which word is noon in ancient Chinese, that is, the word "noon"