nonsense
enormous
Tutelage
Alienate
Emphasis
Yuletide
A noun for garbage meaning "nonsense" could be claptrap or malarkey. The only other common synonym for trash or rubbish that has 8 letters would be foulness.
A synonym for "grateful" that has eight letters is "thankful."
doubtful, unsavory, slippery
forebode, forecast, foretell
Assembly/assemble
deserted?
ten years