How can you use the word "sweetness" to figure out what the word "fullness" means? Decide if they mean the opposite or the same as each other.
Think about what "sweet" means and how it relates to the word "full" in fullness.
They mean the same thing because they both end in -ness.
Think about what the "-ness" in sweetness means--then apply that meaning to the "-ness" in fullness.