Read the sentence. I normally don't mind reading long books, but when I saw the size of the tome that my history professor had assigned for homework, I cried. Which word in the sentence is the best clue to defining the word tome? normally books history professor

The word "books" is the best clue. Immediately after the part where it says "I normally don't mind reading long books", the sentence says "but when I saw the size of the tome ... ", the word "tome" of which is described by "books". So, a tome is a "book".

Note: the definition of tome is actually a very large and scholarly book.

Books, because it defines what type of tome it is which is a book.