This is a great appendix I just came across on the half life of vocabulary in a language. From the text:

The rate of vocabulary change The half-life of a word is the amount of time required for there to be a 50% chance that it will be replaced by a new word. Most words have a half-life of 2,000 years. However, a small number of words have a half-life of greater than 10,000 years. This shows that despite the fast average pace of language evolution, some meanings, like highly-conserved genes, evolve at a slow rate. The y axis in the graphic is the number out of a sample of 200 meanings. (ref. 1)