it's called "semantic range"

Eugene Nida, the widely known linguist who developed the translation principle known as dynamic equivalence, once said that language is a "dictionary of fading metaphors.” Nida was at the forefront of a movement in linguistics that focused on what was being translated rather than the words used for the task. Even when we refer to a tangible object like, say, a "table," the term may have a surprising breath of meaning: we normally eat at one, actions unknown to others are said to be under it, we use it to postpone discussion on an issue, it describes an abbreviated list, etc. When we move into the less tangible realm we find ourselves even less secure. Take the word "fast:” You can run that way, it de­scribes the period of time when you choose not to eat, it's used of colors that don't fade, it describes young people who disregard moral conventions, etc.
       In what sense is a word a "fading metaphor?" Every word serves to represent an object, a sensation, an action, an idea, etc. With use, its semantic range is extended. The original rather crisp image fades and now serves in a number of somewhat similar contexts. As words extend themselves they become increasing less precise. No longer strong, they lose their excitement.
       Language is a remarkable gift to the human specie. From a scientific perspective, the ability of Homo sapiens to communicate at sophisticated levels is one major thing that distinguishes us from other mammals. Of the some 6,800 spoken languages in the world, it is said that English has the largest vocabulary. Google scanned 15 million English-language books and came up with 1,013,913 as the vocabulary number as of January 1, 2012. And we have been adding 14.7 words per day ever since.
       So language is both expanding and fading. We have more and more words, but those words are losing their impact. This poses no particular problem for ordinary life but it does create a serious problem for translating an ancient language. The tendency is to read more into a word that was intended at the time the word was first spoken or written.
       It is not that people can't understand one another adequately. What I am suggesting is that in view of the above considerations, one ought to use language judiciously. Assuming that a person genuinely wants to be understood, clarity and simplicity are the rules of the game. A commitment to integrity in language will make a difference for us in the normal exchange of information, but also for our nation because language is the means for the free ex­change of ideas. When, in the political periods of time, I hear words being used, not to share ideas and come to the best solution, but to win a point at any cost, I find myself wanting to return to the age of sign language . . . not really, but there is a point there. Luther’s comment on the need for “lucid clarity” needs to invade our consciousness in order to help us say what we mean and mean what we say.