My Penguin dictionary doesn't give them as synonyms but it defines them almost identically. I get the impression that nerd is a pejorative term.

"Nerds" has been a common term for socially awkward people for a very long time. A few decades ago, they usually did CB radio communication in their spare time. Nowadays, they handle computers instead.

"Geeks" can be different people.

What precisely does that mean? That some geeks are nerds but not all of them are?

You can be either a geek, a nerd or both a geek and a nerd. None of those are subsets of each other.

And the difference between geeks and nerds and gurus? Gurus earn about 200% more

Only if they're geek gurus. Nerd gurus don't.

https://www.etymonline.com/word/nerd

https://www.etymonline.com/word/geek

Both seem to have fairly pejorative origins.

Still haven't got an answer. What's the difference?

I've always assumed both means this:

From cynwulf's link: https://www.etymonline.com/word/geek

Interesting how the two terms mean different things to different people. Although, if it's "teenager slang", then I think that's not a definitive meaning - it vary's depending on the teenager's own meaning of it. In other words: it's just "slang".

But all that said, I've never given it a lot of thought...

"The difference being geeks are employable."

That is, as far as I recall, the wording of an aside in a magazine article from years ago, almost certainly in New Scientist.

I took it to mean that geeks have more rounded and useful knowledge than nerds, implying that nerds are more hobbyists and geeks more professional. I don't think that's authoritative but I have thought of it that way ever since, for example I would describe myself as a Linux nerd, but a kernel developer as a Linux geek.

Of course there's massive overlap between those two definitions, especially in things like FOSS and shipbuilding (ship geeks built the Titanic, nerds built the Ark).

When I use a word,' Humpty Dumpty said, in rather a scornful tone, `it means just what I choose it to mean -- neither more nor less.'

I know Bill Gates was considered a nerd as a teenager. But he was hardly unemployable.

Gates was the nerd, Allen was the geek. Good enough for you ?.
Similar for Apple I guess.

So far as I can tell - no important differences. It's a matter of interpretations...

It's also a matter of "labels". In popular culture, film and the media, "hacker" means something else to what it really means.

So for a non technical person you're a geek/nerd if you're doing something which they can't understand easily or find cryptic.

You're also a "geek" if you wear a certain kind of fashion... so what does the term really mean? Not a fat lot.