In my studies, I have found that the correct meaning of the word is the meaning that the author intended. In this case, Paul the Apostle is defending his gospel, which includes the doctrine of Resurrection. In this context he is answering two questions, "how are the dead raised? With what kind of body will they come?" The second question seeks information concerning the kind of body given to the resurrected; the first question is concerned with the means by which the body comes into existence.
At this point in the argument, Paul will attempt to bracket the concept by pairing up contrasting qualities of the resurrected body or at other times pairing up contrasting agencies of production. It's important to bear in mind that each pair answer to the same question.
42 It is the same with the resurrection of the dead. What is sown is perishable, what is raised is imperishable.
The contrasted pair above is perishable :: imperishable, which answers to the question "what kind?"
43 It is sown in dishonor, it is raised in glory;
The contrasted pair above is dishonor :: glory. I believe this answers to the question, "what kind",which suggests our sinful nature. All sinners die in dishonor, because death itself condemns us as a sinner. Glorification, then, is the transformation of the sinner into a glorious, righteous, good, person with moral courage. And the agency of this transformation is God himself
it is sown in weakness, it is raised in power;
The contrasted pair above is weakness :: power. This contrast is reminiscent of Romans 8:1-4, which answers to the question of means. What the law could not do because of the weakness of our flesh, God did by sending his own son, and etc. Again this is a contrast of agency: what we can not do for ourselves; God has done for us.
44 it is sown a natural body, it is raised a spiritual body.
Here is our verse, the one in question.
The contrasted pair above is natural :: spiritual. While the term "spiritual" can answer to the question of kind, natural answers to the question of means. Te term "spiritual" stands in contrast to "natural", not "physical". Therefore, the definition of "spiritual" is the opposite of "natural."
Paul often uses the word "natural" to indicate the way things exist and function in nature. So for instance, in Romans 1:26 he says, "For this reason God gave them over to degrading passions; for their women exchanged the natural function for that which is unnatural, " indicating a contrast between what nature normally expects, i.e. a woman sleeps with a man, as compared to that which is unnatural, i.e a woman sleeps with another woman.
If there is a natural body, there is also a spiritual body.
The contrasted pair above is natural :: spiritual. This pair contrasts the body which nature provides and the body which God will provide. Animals are born into this world, with a mother and father that nature provides. The body of this animal is its natural body. This answers to the question, "from where did this body come"? The natural body comes naturally from a mother and father.
A "spiritual body" by contrast, is a miracle body that God provides apart from the natural processes of physics and chemistry and biology. "Spiritual" in this context means "supernatural", i.e. brought into existence by God outside of the normal processes.
