"When I use a word," Humpty Dumpty said, in rather a scornful tone, "it means just what I choose it to mean—neither more nor less."
I had one of those "annotated" editions of Through the Looking-Glass where "notes" occupied about 1/4 of each page
on average. The note to the sentence you quoted said something to the effect that that was, in fact, Lewis Carroll's "official position" on the meanings of words.
We may or may not agree with such approach, but it definitely explains language changes over time, including the one with the word "explorer".