There is a difference though. All the other examples you mentioned are words whose meaning has changed over time. The older meaning has gone out of favor for the newer one. Still one meaning though. You mention gay in today's world and most everyone knows what you are talking about. Trinity, though has not just changed with time. The definition has also multiplied to the point that one really does not have a clue what someone is referring to without asking for further information that explains their spiritual/religious stance.