The usual full expression is something like “probable cause to believe that the person to be arrested has committed a particular crime”.
> "Probable cause" can be used to justify a search.
“Probable cause” is a constitutional requirement for search warrants, arrest warrants, warrantless arrests, and warrantless searches; for searches, the probable cause is that the search conducted will uncover evidence of a crime, which is different than the probable cause for arrest.
> You would need to actually be suspected of a crime.
Well, no, there needs to be probable cause to believe you've committed a crime. Actual suspicion is a much lower standard.
> If the cops don't find drugs, what crime are you guilty of?
There are...like thousands of other crimes, and millions of possible configurations of things that are not drugs that could support probable cause to believe you've committed one of them. Spray paint cans consistent with a recent spate of vandalism (graffiti) in the area is one I’ve personally seen used, beyond things that are inherently actual or apparent contraband, and the “actual or apparent contraband” category extends to more than just drugs.
In america you can be hauled in and convicted of nothing more than "resisting arrest", with no other prior crime or suspected crime. If a cop tries to arrest you and you do ANYTHING other than comply, that's a crime
You would need to actually be suspected of a crime. If the cops don't find drugs, what crime are you guilty of?