截然不同 (jié rán bù tóng): แตกต่างอย่างสิ้นเชิง

The cultures of these two cities are entirely different: one is traditional, the other modern.

Their views are entirely different, and it's hard to reach an agreement.

The personalities of these twins are entirely different: the older brother is outgoing, the younger is introverted.

The lifestyles of the past and present are entirely different; technology has changed everything.