I'm looking for a dictionary that contains definitions for lots of advanced maths terms like Lie Groups, Galois Theory, Green's Function, operators etc. Preferably the definitions be relatively easy to understand (for A level/university students) and without too much jargon. I've found one just called "Mathematics dictionary" by Robert James. Is that any good? Are there any you would recommend?
I'm asking this because I'm finding it impossible to learn about more complex topics on Wikipedia without going into an infinite amount of rabbit holes trying to understand the terms they use. The simpler version of wikipedia is great but isn't there for most advanced topics. Any alternative advice would be welcome!