Is there a word for 1/3? So I know that in Mandarin, 1/2 is 二分之一 or 一半. Is there a similar word to 一半 for 1/3? I mean, instead of 三分之一, something like 一——？
因為十進制在中國已被使用了很長的時間，故比較少分數字詞；其中只有「半」作為單字詞，於中國古代應用如下。
Because the decimal system has been used for a long time in China, there are fewer fractional words.
半 is the only single word, which was used as follows in ancient China.

1/2 one-half 半、中半
1/3 one-third 少半、小半
2/3 two-thirds 太半、大半
1/4 one-fourth, a quarter 弱半
3/4 three-fourths, three quarters 強半

中國數字分數系統中，稱呼分數時，先稱呼分母，後稱呼分子。
In Chinese fractional system, the denominator is addressed first, and then the numerator.

例如：其亡者三二 (Two-thirds people died)。

Source: 中文數字