The origin of the name is even sillier.

In 1849, a pharmacist called Garot discovered a new sugar, that gives rhubarb stalks that red colour. They proposed the name "erythrose", because "ἐρῠθραίνω" erythraínō means "to redden" in Greek, and you got to have that -ose for sugars. Fine name, right?

Later on, it was discovered erythrose was two substances: one a mirrored version of the other. So they got named D-erythrose and L-erythrose.

But then half a century later, a chemist called Otto Ruff discovered another compound. Same atoms as both D- and L-erythrose. Same chemical bonds: C goes to O that goes to H etc. But it was neither identical to the erythroses, nor a mirrored version of them.

So Ruff picked the prefix erythr-, clipped the -ry-, and jumbled the leftover letters — because the new compound was like a jumbled erythrose. Then he added the suffix -ose, and you got "threose". And guess what, later on it was discovered threose was two compounds.

For reference, here's the chemical structure of all four molecules. The bonds looking like thick triangles have atoms closer to the viewer than the rest of the molecule, and the dashed bonds are for atoms further behind.