[mnbvkhgvmj]

This depends upon where you are doesn't it? In the UK the grounds for arrest are "reasonable suspicion" in the US isn't it "probable cause"? I think that "reasonable suspicion" is similar to 10% certainty and "probable cause" 25% (c/f with "beyond reasonable doubt" which should be 95% certainty)...

I am not a lawyer. If anyone is in doubt I suggest speaking to a lawyer!

[azernik]

"Probable cause" is defined using the word "reasonable" in lots of sources. The root of any UK/US difference is more likely related to drift in precedent over the last couple of centuries than to any precise difference in the meaning of words.