That’s not bad. Remember though that words often have more than one meaning, and in this case you’ve only covered one of the meanings.
Become a contestant on the $64,000 pyramid or Password.
You gave two different things: a synonym and an explanation. Both are valid definitions.
As Isamu said, try to come up with definitions for the other meanings of “material”, for other meanings of “substance”, and with other synonyms. See if you can find a few antonyms too.