This is community wiki. In each answer, please list one word at the top and below that list as many different meanings of that word in mathematics as you can think of, preferably with links or definitions. ("Adjective" and "adjective noun" count as the same adjective.) People should edit previous answers as appropriate.
(This is mostly just for fun, but I'm also curious if there have been successful attempts to rename concepts that involve overused words.)
Edit: I may have been slightly unclear about the intent of this question.
- When I say "overused" I don't mean "used too often," I mean "used in too many different ways." So I'll change the title of the question to reflect this.
- Different concepts named after the same mathematician, while potentially confusing, are understandable.
- I mostly had in mind adjectives that get recycled in different disciplines of mathematics. Different uses of the same noun tend to be less confusing, e.g. the example of "space" below. I think it's good to be intentionally vague about what we consider a "space."