An author commits the fallacy of equivocation when he uses two or more definitions of a word interchangeably, as though they were identical.
In syllogistic logic, the equivalent fallacy would be the fallacy of four terms.
Puns work because they are deliberate uses of equivocation. In Romeo and Juliet, for example, Romeo's flippant friend Mercutio is mortally wounded by his enemy Tybalt. Mercutio remarks that "to-morrow . . . you shall find me a grave man" (III.i.97-98). Grave means either "serious" (in contrast to Mercutio's usual levity) or "burial plot" (because Mercutio will soon be dead).
Fallacious equivocation, however, is usually much more subtle, and obviously more dangerous than innocent wordplay. Years ago, on the moribund KJB Vs The Modern Version group on Yahoo, I made a remark to one particularly short-fused KJV-onlyist named George Calvas about believing in "the actual God of the actual Bible," or words to that effect. In response, poster "warrior_of_the_sword" asked: "And that would be WHICH BIBLE according to you?" To this, I answered that I was unaware of there being more than one.
This is a subtle example of the fallacy of equivocation. When I referred to the Bible, I meant the literary work known as "the Bible": the anthology of Jewish and Christian works comprising the 66 books from Genesis to Revelation. However, when "warrior" asked me "WHICH BIBLE" I meant, he used the term to mean a particular edition, translation, or version of that literary work. Put another way, my use of "Bible" was universal; his was particular.
Here's another one. KJV-onlyist author Timothy S. Morton has an online book titled Which Translation Should You Trust? A Defense of the Authorized King James Version of 1611. In a section named "Are Translations Inferior?" he attempts to argue that a translation can be superior to its source text by appealing to the Bible:
Another fact concerning translations is that in the three verses the word "translate" (or forms of it) is found in the Bible, the object translated is BETTER than it was to start with! . . . The first verse is 2 Samuel 3:10. There, the kingdom is to be "translated" from the house of Saul to David. When one reads the context of this passage, and of the reign of David after, he finds the kingdom becomes better than it was in its original state! . . . The second translation is found in Colossians 1:13. The translation here is the conversion of a lost sinner to the kingdom of Jesus Christ. No Christian can say this is not a translation for the better! The last mention is in Hebrews 11:5 where Enoch is spoken of as being "translated." Again, no believer in his right mind can say a person would not be better off to bypass death and go directly to Heaven. . . .
As mentioned before, we agree that no translation can be "word-perfect" with the original, but this in no way means, as scholars assume, that a translation is of a lesser quality. It could just as easily be (as we have just seen) BETTER in quality than the original! The word of God does NOT lose its purity and authority by being translated.1
Here's the problem. In the English of the KJV, the word "translate" is synonymous with the word "transfer." In 2 Sam. 3:10, the "translation" is a transfer of power: Saul's kingdom was given to David. In Col. 1:13, it is a transfer of citizenship: from the kingdom of darkness to the kingdom of the Son. Finally, in Heb. 11:5 it is a transfer of location: Enoch was removed from the earth and brought, body and soul, into heaven.
In no case in the KJV does the word translate mean, for example, to render a text or speech of one language into another language. When the Bible referred to that kind of "translation," the KJV translators used a form of the word interpret (see, for example, Matt. 1:23 and John 1:41). To say that since Enoch was "translated" to a better place, therefore the KJV as a translation is superior to the texts it was translated from, is an equivocation, and therefore sophistry.
Show how your opponent has redefined a term. Demand that he defines how he is using that term, and make sure he commits to that defition. If he wavers between meanings, call him on it.
1 Timothy S. Morton, "Which Translation...II," PreservedWords.com, http://www.preservedwords.com/kjv2.htm (accessed January 5 2010).