As adjectives the difference between accessible and available is that accessible is easy of access or approach; approachable while available is such as one may avail one’s self of; capable of being used for the accomplishment of a purpose.
Meaning that "accessible" is something that you can get or use, when you "access" something you reach it out or use it for some reason, so it must be something you can use
But on the other side of the spectrum, "available" has a wider meaning than "accessible", it means something you can use, reach out, do, or feel free to take
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