Latin root fus means pour
Comes from Latin fundere which means pour, melt, inject, fill, irrigate, gush, etc. The first idea is the object is about liquid stuff, it can be water or metals in liquid state. The second idea is the action of fus is unthoughtful(kind like no brainer), without careful scrutiny and check, unpurposeful, when you use it to describe the huge amount of something, you mean there is quantity but no quality, the more doesn't mean better, it's usually negative. Say you got a profusion of information, it means there are a lot of information but most of them are just garbage and junk like many things on internet, the sheer quantity doesn't mean there are really useful for you, that's why we need Google and Facebook recommendations, without it we will get lost in ocean of information. Think about what it feels like to drink from the fire hose.
- A Russian security think tank, says the profusion of armed robots is slow, as many get no further than the proposal stage.
In this sentence the profusion means the speed to adopt armed robots to proliferate it is slow. It should be slow, armed robots are autonomous killing machine, it has some serious ethic controversies, the profusion of it is doubtful and should be considered carefully.
Let's see the word confusion, con means together, like mentioned above, gather a lot of things together without careful check and critical thinking, the only result is confusion. Human brain is not good at processing a lot of things at the same time, that's not how human brain works, it must learn things step by step, each time with a small piece of it and gradually you learn stuff.
Refuse can be considered as reject when the root fus can means injection. Re means back, the difference is the intensity of tha action. Refuse means throw back, you can throw with bare hands, it's informal, not so purposeful and coarse-grained. The employee refused the position. He didn't ask for the position but was offered with the position, he react with refuse. The action ject is more intense, in English the word shoot is a better choice to describe the root ject. To shoot you need at least some kind of apparatus, a needle, a gun, a rocket thruster and you did it in a purposeful and formal way, you are serious. When you refuse, there are possibilities to accept it, when you reject, you never even thinking about the possibility of accepting.
If you are an editor, censor, authentiactor, auditor, you reject the submission from someone if you consider it's not qualified. It will be weird to use refuse here. Use reject when you are in charge, you the boss, you have some kind of authority, use refuse when you are under charge, or you are the one who is given an offer.