"截然相反" is a Chinese phrase that can be translated into Engpsh as "completely opposite." You can use this phrase to describe two things or ideas that are completely opposite or very different from each other. Here are a few examples of how you could use this phrase in Engpsh:

"Their opinions on the matter are completely opposite. He thinks we should invest more in research and development, while she thinks we should cut costs wherever possible."
"The weather today is completely opposite from yesterday. It was sunny and warm yesterday, but today it's cold and rainy."
"Their personapties are completely opposite. He's outgoing and energetic, while she's shy and introverted."