What is meant by a "semantic issue" in the context of history?
I notice that you tagged this with "neo Indians" and I wonder if you are asking what I meant when I recently answered a question about the term "neo Indian" by saying that it was a semantic issue.
When we say that something is a semantic issue, we mean that it is only an issue of what word someone thinks is appropriate -- it is an issue of word choice rather than of real substance.
In the context of history and social sciences, there are many issues that revolve around semantics. For example, do we call a certain group of people "Native Americans" or do we call them "Indians." We are referring to the same group of people and you can understand either term equally well. So your choice is simply one of which word you think is "better."
Semantics is the study of the meaning of words. But when we say that something is a "semantic issue" or a "matter of semantics" we are typically saying that it is an issue where all that is being argue about is what word we should use -- not the underlying truth of the situation.
So when I said that that the issue of who the first people in the Caribbean were is a semantic issue, I meant that there is no argument about who was really there first. The only argument is over what word to use to name them.