Words change their meanings over the years; sometimes deliberately and sometimes accidentally. Examples of accidental change include "tissue" (or, as we called them when I was a kid, snot-rags) becoming "Kleenex", or "reproduction" becoming "Xerox"- those brands had such a huge market share that the specific became the generic.
Examples of deliberate change include "Gay", "African American", and "Native American"; they were chosen because the previous terms had become pejorative. The first two mentioned have actually had several generations of change, and may change again in the future.
None of those changes matter very much to the common comprehension required for communication- if I say, "Hand me a Kleenex", my meaning is clear. A person who was unfamiliar with the term "Native American" could easily figure it out, and the only people I've known who were genuinely confused by the term "African American" were the young children of a white immigrant from South Africa. Other words that have changed, however, are becoming a true hindrance to clear communication. Here are a few:
Literally The way the word is used today, one would think that people literally do not know what it means.
God At one time, "God(s)" meant a supernatural being or beings. Discussions of "God" were limited to the quantity (Unity? Trinity? Poly?) of these beings, and the attributes thereof. Today, people speak of God being love, or the interdependent web, or some such. Of course, we know why these circumlocutions were invented- to allow Catholic and Anglican bishops who had lost their faith to continue to draw their stipends. But it has resulted in much miscommunication.
Liberal and Conserative, and to a large extent Democrat and Republican One small example among many: originally it was Liberal Democrat Kennedy who championed massive tax cuts to stimulate the economy, and Conservative Republicans who opposed it as a risky scheme. This was not a deliberate change, but merely reflects the fact that most politicians are not leaders but weathervanes. Nonetheless, it is rendering true communication difficult.
Socialist, Fascist, Nazi The original dictionary definitions of these words are no longer used outside of a polysci doctoral thesis; today they merely mean "Someone I don't like". The only difference remaining is in who is speaking: Democrats call those they hate "Nazi"; Republicans call them "Socialist", and conspiracy nuts call both of them "Fascist".
What words would you add?