期

The mainland Chinese says Monday (星期一) as "xing1 qi1 yi1", whilst Taiwanese pronouces it "xing1 qi2 yi1". Difference lies at tone of 期.

The mainlanders apply the 1st tone and the islanders take the 2nd tone.

China: 　延期 [yan2 qi1]，过期 [guo4 qi1]
Taiwan: 延期 [yan2 qi2]，過期 [guo4 qi2]