If a cat’s meowing is getting on your nerves, here’s one thing that won’t work: telling him to stop. Cats respond to sound with more sound. By telling a meowing cat, “Stop!” or “Shut up!” you are making sure that the “conversation” continues.
The only way to silence him is give him what he wants—food, water, attention or an open door. (On the other hand, if it’s a female cat caterwauling because she is in heat, you won’t be able to give her what she wants.)