Is summer three or four tones?

Read it three times in summer. chǔ shǔ。

By looking up Modern Chinese Dictionary, it is found that the pronunciation of "Chu Shu" is three tones, but why it is not explained in the three-tone dictionary. Generally speaking, as a place or unit, "Chu" is pronounced four times, and the rest are generally pronounced three times, such as "Fangzi". In the dictionary, "early summer" is a proper noun of one of the 24 solar terms.

The arrival of the hot summer also means entering the second half of the month. Shen Yue is the first month of autumn. Although it feels like autumn, the heat of summer is still unabated. Summer is a solar term reflecting the temperature change. "Summer" means that the hot summer is over. ""Go, go, and the summer heat will stop here. " It means that the heat is about to pass.