There are anywhere from 400,000 to a million words in the English language, and they can be organized in any number of ways.
One of the latest is to divide words into three tiers.
- Tier One consists of the basic words. These are words like book, girl, and dog and usually have only one meaning. There are around 8,000 word families included in Tier One.
- Tier Two words are high-frequency words that often occur in mature-language situations such as adult conversations and literature, and therefore strongly influence speaking and reading, especially by allowing detailed descriptions. They usually contain multiple meanings. Good examples are masterpiece, fortunate, and benevolent.
- Tier Three consists of low-frequency words that occur in specific subjects in school, hobbies, occupations, geographic regions, technology, weather, etc. They are usually learned when a specific need arises, like learning amino acids for chemistry. Examples include economics, isotope, and asphalt.
The significance of these divisions is to give teachers a better understanding of what words to emphasize. Students will normally learn Tier One on their own; Tier Three can be taught on an as-needed basis. So the key is Tier Two with the multiple meanings.
This will also impact testing. The SAT originally measured memorization of word definitions. New versions of the test will concentrate more on context, as in evaluating claims in reading segments and how a student evaluates them.
It will be interesting to see just how far this new approach takes us.
A good basic explanation of the tiers is at https://www.superduperinc.com/handouts/pdf/182_vocabularytiers.pdf.