A good way to remember the meaning of the “negative” in negative reinforcement is to think of it in relation to mathematics. When you see a negative symbol in math then it means subtraction.
When you see the term negative used with reinforcement then think of something being subtracted.
Consider someone taking a shower to remove a bad smell; you could say taking the shower led to the subtraction of the bad smell or said another way, taking the shower was negatively reinforced by the removal (subtraction) of the bad smell.