" There are no ethnic or racial overtones for the term-the implication is that the person's head has more bone than brain. Thus, if someone seems to use his brain less, he will be called bonehead. Other definitions of this term include stupid, slow, stubborn; ridiculously simple; seemingly idiot proof; and functioning at a Neanderthal level of complexity. Thus, bonehead can be used not only to refer to a specific person but also on things.
The definition of a term in a society is mostly dependent on the familiarity and connotation with common objects. In the case of the "bonehead," its meaning and formation is based on the fact that a human's head is composed of bone and brain. Since brain symbolizes knowledge and intelligence, bone is connected to its opposite.