I believe that the "hard" actually refers to the fact that such trees have a harder shell for their seeds. From wikipedia [1] Hardwood is wood from dicot angi

I believe that the "hard" actually refers to the fact that such trees have a harder shell for their seeds. From wikipedia [1] Hardwood is wood from dicot angiosperm trees. The term may also be used for the trees from which the wood is derived; these are usually broad-leaved. In temperate and boreal latitudes they are mostly deciduous, but in tropics and subtropics mostly evergreen. Hardwood contrasts with softwood (which is from Gymnosperm trees). Hardwoods are not necessarily harder than softwoods. In both groups there is an enormous variation in actual wood hardness, with the range in density in hardwoods completely including that of softwoods; some hardwoods (e.g., balsa) are softer than most softwoods, while yew is an example of a hard softwood. [1] https://en.wikipedia.org/wiki/Hardwood https://en.wikipedia.org/wiki/Hardwood