fault line
noun
1- a line on a rock surface or the ground that traces a geological fault（岩石表面或地面的）断层线。
1.1
- a divisive issue or difference of opinion that is likely to have serious consequences（可能引发严重后果的）分歧; 裂痕：
religion is now the great fault line of American politics.
宗教现已成为美国政治中可能引发重大分裂的问题。