As someone who has both played in a band and composed video game music, I can tell you that describing music to others is quite difficult. Or more specifically, describing something and then having the other person try to play or write it. Musical adjectives can be really vague... words like "warm", "funky". "plodding", and "crunchy" might be used, but their meaning hits a little different for every listener. Even among trained musicians, interpretations can be wildly different. I once asked a sound engineer to make my bass track "crunchy," but what he came back with just sounded "thin" to me. And I realized, I had given him this word that could make him think of something very different than what I would think.
The point is, you will never be able to perfectly describe the sound you want. Just give it your best shot and like others said, provide images and other reference material. The revision period is really important to get what is hopefully a decent track, closer to your ideal track.
It might help you to read a little bit about technical music terms, which will mostly be lost on non-musicians. Basic knowledge of things like wet vs dry, compression, dynamics, and harmony will make understanding each other easier. But, it's not absolutely necessary. Just know that you'll need some trial and error to get results that both parties are happy with. And at the end of the day, if you are paying for the work, you get the final word on what is acceptable. I worked with someone who thought a specific sound was not fitting right. To me it was just a background noise and I didn't see why it was inappropriate for the game. But, they insisted on its removal and so I did with no further argument. You should expect the same from your composer.