"The qualities of trees vary exceedingly, and are very dissimilar, as those of the oak, the elm, the poplar, the cypress, the fir, and others chiefly used in buildings. The oak, for instance, is useful where the fir would be improper; and so with respect to the cypress and the elm. Nor do the others differ less widely, each, from the different nature of its elements, being differently suited to similar applications in building."
Marcus Vitruvius Pollio, De Architectura, Book II, Chapter 9
Lumber is wood from trees, and it is used in ways in which the character of the material remains essentially as it was in its natural state. So, rayon and acetate, which are made from wood, are not lumber products but are synthetic fibers, while glulam ...