Many places worldwide, these two terms are being used interchangeably. However, there are some regions that make certain distinctions between the two.
In most cases, timber is said to be the wood that is currently erect and is attached firmly to the earth’s ground. This is the term used for a tree that has not yet been processed into lumber. On the contrary, lumber is generally accepted as the wood that is no longer attached to the ground and is often seen as the laid down or processed wood.
Secondly, timber is usually the term used for a piece of wood that still has its bark on whereas lumber is usually bark-less in nature. The latter usually undergoes a drying process and has a firm finish to it. Lumber is often prepared with accurate measurements and is almost always ready for use in construction and furniture making.
Depending on the country, timber is the common name used for wooden boards. In the U.K. and Australia whereas lumber is the one used for the same kind of product in the U.S. and in most parts of Canada. In this same region (U.S. & Canada), they adopt the term timber for a piece of lumber with a relatively small measurement of no less than five inches or 127 mm. For them, timber is also the non-processed standing wood.
Due to its processed or finished nature, it is the word ‘lumber’ that is dominantly used for commercial purposes and sale. For timber to be made commercially available for construction, it is usually necessary for it to undergo finishing first before it is sent to the market.
In history, it can also be accounted for that timber is the earlier word to be formulated and used by the masses.