Agreed. From now on I will use blackmail to refer to extortion involving the threat to reveal incriminations, and if I encounter confusion, I will either direct them to this discussion or use rhetoric / appeal to my own authority to convince them of the truth of my position, depending on which I judge to have the better chance of actually convincing them.

Sorry to be so formal and spell it all out, but I just recently worked this unconscious process out and I am bursting with enthusiasm to share it!

(Note that the field of linguistics uses the phrase 'perfect synonym' to refer to what you mean by synonym, and when they say synonym they allow possible variances of nuance. Note also that I think their definitions are not in touch with the definitions for 'synonym' that people actually use, so more fool them.)