Probe vs. investigation

“Probe” itself is a noun referring to a type of surgical instrument used to examine different parts of the body. “To probe” has a similar meaning to “to investigate” but usually refers specifically to examination that is more deliberate, invasive, or rude. A great example is when someone is asking questions, but being pushy and rude about it. In this context, one could say that they are probing for information.

There is shockingly little difference between the two. "Probe" as a synonym for "investigation" does come from a probe tool used in medicine, but this is just figurative. The two are practically interchangeable in that sense. "Investigation" is probably more common, but "probe" comes up most often in newspapers and other old news media, especially when a government is doing the probe or the target of a probe, for example "corruption probe", "antitrust probe", or a "probe into Chinese turbine companies." Still, the same articles will use "investigation" for the same thing. Probe can also be used a verb as in "EU probes Facebook over misinformation", while investigation has a verb form in "investigate." I would also say, however, an investigation into something other than corruption, financial crimes, or corporate crime is almost always an investigation and never a probe. For example, a "murder investigation" or an "investigation into claims of stalking" would never be called a probe. By and large though, they have identical meanings, and use of a tool is not required to call something a probe.

In the USA, probe can mean a high level investigation into something serious, whether civil or criminal. This usually involved multiple people. "Investigation" can be used interchangeably. However investigation can also be used for something as a traffic stop that goes wrong or bar fight. "Why am I being detained officer? Because I'm conducting an investigation". Probe would never be used here. Of course probe has a few other definitions, both verb and noun.