Is the word novel a common noun?

The word "novel" can be both a common noun and an adjective. It depends on the context:

Common Noun:

* When referring to a long fictional narrative: "I just finished reading a great novel about a detective."

Adjective:

* When describing something as new or unusual: "This is a novel approach to solving the problem."

So, to answer your question directly, "novel" can be a common noun when it refers to a specific type of book.