This was prompted by a word used in a thread.
Why is it words change meaning? For instance, the word "decimate" at one time meant "to reduce by 1/10th". Now it is used (and even some dictionaries have this as a meaning) to "destroy a great number of".
Now we can argue if 10% is a "great number" or not, but the common usage is more along the lines of completely destroy.
Then there is the word "racism" that is used any time someone makes a less than flattering remark about someone of a different race. It is even used when there is discrimination based on race---that does not necessarily mean it is racism.