The word 木头 is formed through a straightforward conceptual combination: the first character 木 means "wood" or "tree", denoting the material itself, while the second character 头 serves as a nominalizing suffix that often indicates a concrete, tangible object or piece derived from the root concept. Thus, by attaching 头 to 木, the abstract idea of "wood" is transformed into the concrete, everyday object we understand as a "piece of wood" or "lumber".