Yes, much is a Scrabble word!

Adverb

1. To a great degree or extent

2. Very

3. To a very great degree or extent

4. (degree adverb used before a noun phrase) for all practical purposes but not completely

5. Frequently or in great quantities

Adjective

1. (quantifier used with mass nouns) great in quantity or degree or extent

Noun

1. A great amount or extent