Obsolete, adjective. No longer produced or used; out of date.
I have noticed in the “King James Version debates” that certain words are often described as obsolete. While no one should deny that there are difficult words in the King James Bible – either because they are just difficult in the general sense, or because they are words no longer frequently used in conversation, or because they are words whose meaning in the Bible are not the same as what modern English speakers usually think of today. However, the term “obsolete” is not the best way to describe these words. (See above definitions.) While the semantic range of these words may “allow” one to use obsolete, notice how carefully Dictionary.com restricts their use of obsolete.
In Dictionary.com, the archaic label is described this way: “Archaic is used as a label in this dictionary for terms and definitions that were current roughly as late as 1900 but are now employed only as conscious archaisms.” It describes the obsolete label thus: “Terms and definitions labeled Obsolete in this dictionary have not been in widespread use since the mid 1700s. Unlike some relatively familiar archaic words and phrases, like prithee and thou art, obsolete words and phrases are not easily understood by a modern reader, and obsolete senses of current terms.”
When we consider that the King James Version of the Bible has been in constant use in English-speaking nations from AD 1611 to the present, it should give us pause to think of its words as obsolete! If you mean “hard to understand” just say that. Every Bible has some words that are hard to understand. If you mean “specialized language” that is theological just say that. Maybe obsolete could be retired? I find it difficult to consider words I have been reading in my Bible and hearing in church all my life as being “obsolete” – no longer used.