Timber and lumber are basically wood and they mean the same thing.
Timber/lumber is wood used as building material, or a tree considered as a source of wood instead of as a plant. It can also mean a beam or a person who is a timber, thought the person meaning I've not heard of much.
Answer
Timber is usually the wood as it grows or is felled. Lumber is the wood after it is milled and ready for use.
Lumber and timber are closely related terms, but their usage depends on regional language. In many countries, especially Australia and the UK, “timber” refers to wood that has been processed and prepared for building, while in the United States, the same material is commonly called “lumber.” Both describe wood that has been cut, milled, and graded for construction or manufacturing purposes. You’ll often see this terminology reflected in businesses such as Timber Yards Sydney, which supply what Americans would call lumber—framing wood, treated pine, and structural materials—under the broader category of timber.
Timber is to lumber as quarry is to stone because timber is where cut lumber comes from and a quarry is where cut stone comes from.
People buy "timber" as an investment. Timber is uncut lumber. People buy lumber because it is an excellent building material and is renewable.
Lumber
The harvesting and sale of raw lumber\wood (a.k.a. Timber)
Lumber jacks.
Pressure treated timber is timber impregnated with chromated copper arsenate under pressure and vacuum cycles. These preserve the timber from various fungicides that would normally eat the timber reducing its life-span.
A lumber is that person who falls timber. The activity is called lumbering.
Lumber or timber.
lumber
iron and lumber [timber]
The answer is "lumber".