In dog training, simple commands work better than complex ones
What you are trying to do in using simple one-word commands is to create a habit in the dog. Canine behavior, like that of humans, has a lot of habitual aspects to it. When you train dogs with simple commands, they are easier for the animals to hear and recognize the meaning than if they have to pick out the words from your steady flow of speech.
We do all know that dogs are prone to noticing words they recognize when you are talking with another person. Let's say that you ask your partner, "Honey, would you mind taking Buddy for his walk? I'm so tired!" Chances are high that Buddy's tail will start wagging as he hears his own name and that word dogs love so much, "walk."
So use one-word, easily pronounced commands -- which, by the way, are also sometimes called cue words. That expression gets away from the idea that you have to be the boss and the dog has to obey! While there are certainly times that do call for obedience, such as when you need the dog to come rather than go into the street, by and large the best dog training evokes willing compliance from the dog.
When you are starting to teach a puppy, that's an important time to use simplicity in your words. Sit, come, stay, down... these words are tried and true training commands.
But what to say if your dog is about to jump on you? Don't use "down" since that has a different meaning, the idea of sinking to the floor. In this case, use the simple command "Off!"