[yellowapple]

"taking a bank robber’s loot and giving it back is not theft."

I mean, that is technically theft. It's just very obviously justified theft in response to a previous theft (assuming you prove beyond a reasonable doubt that it is in fact the bank robber from whom you're taking the money).

[IAmEveryone]

It's not. Here's the definition from wikipedia: " theft is the taking of another person's property without that person's permission with the intent to deprive the lawful owner of it"

...but that's really not the point here, is it?

[yellowapple]

No, it's not the point at all. I just like going off on these sorts of weird tangents :)

Curiously, Wiktionary has a different definition: "The act of stealing property". "Property" in turn has a lot of different definitions, the first being "Something that is owned". Relevantly, neither definition specifies by whom the property is owned; as long as it's someone's property, stealing it is technically "theft" under this sort of broad definition.

Merriam-Webster seems to agree more with you than it does with me ("[...] the felonious taking and removing of personal property with intent to deprive the rightful owner of it" / "an unlawful taking [...] of property"), while Dictionary.com seems to be similarly vague ("the act of stealing", though this is lumped in with "the wrongful taking and carrying away of the personal goods or property of another" and "larceny").