8" long and 8" in diameter?? It doesn't look like equal height and width to me...
What ever it is its badly etiolated. See how the top is skinny and tapered? Thats from not enough light, and it will always be skinny and weak in that point. If you bought it like that I'd take it back and get my money back because who ever grew it doesnt know what they're doing. Its either compost, or chop the top off and hoe it comes away with multiple branches.
There's lots of stuff that really shouldn't be posted on a fish forum.. but it's callled the lounge.. Some people have other interests besides fish and look to help from friends first rather then joining another forum...
I'm not 100% sure but it looks like one of the cereus family to me but, I don't have any idea which it is or even if I'm right. Lol, if it were an orchid, palm or cold hardy tropical I'd have a lot better idea mate.
hth
Max