1. PROBLEM and ISSUE - 'Problem' is used when you want to convey that you want to solve something. 'Issue' is a little more formal and conveys that you want to talk about "bigger problems" such as world hunger. It also has its own phrases that it's used with, like "to take issue with something". Sometimes, however, the two can be used interchangeably, such as here: "There's an issue with my computer" or "There's a problem with my computer". 2. THING and STUFF - 'Thing' is more used for one object, whereas 'stuff' is used to refer to more than one.