Is this a correct implementation of Comparator?

Question

I have a class, Word, that has a String representing a word and an Enum representing the difficulty of the word. Then I have another class, Vocab, that has an ArrayList of Word-objects. I want to sort my ArrayList by either difficulty or by the alphabetical order of the word.

I figured I should use a Comparator, and here is how I did it. All classes are in the same package:

Diff:

public enum Diff {
   EASY, MEDIUM, HARD;
}

Word:

public class Word {
   private String word;
   private Diff diff;

   public Word(String word, Diff diff) {
      this.word = word;
      this.diff = diff;
   }

   public String getWord() {
      return word;
   }

   public void setWord(String word) {
      this.word = word;
   }

   public Diff getDiff() {
      return diff;
   }

   public void setDiff(Diff diff) {
      this.diff = diff;
   }

   @Override
   public String toString() {
      String string = getWord() + ", " + getDiff();
      return string;
   }
}

Vocab:

public class Vocab {
   private ArrayList<Word> words;

   public Vocab() {
      words = new ArrayList<>();
   }

   public void sortByPrio() {
      Collections.sort(words, prioCompare);
   }

   public void sortByName() {
      Collections.sort(words, nameCompare);
   }

   private Comparator<Word> prioCompare = new Comparator<Word>() {
      @Override
      public int compare(Word w1, Word w2) {
         return (w1.getDiff().ordinal() - w2.getDiff().ordinal());
      }
   };

   private Comparator<Word> nameCompare = new Comparator<Word>() {
      @Override
      public int compare(Word w1, Word w2) {
         return (w1.getWord().compareToIgnoreCase(w2.getWord()));
      }
   };

   public void addWord(Word newWord) {
      words.add(newWord);
   }

   @Override
   public String toString() {
      String string = words.toString();
      return string;
   }
}

Main:

public class Main {

   public static void main(String[] args) {
      Vocab myWords = new Vocab();
      myWords.addWord(new Word("Apple", Diff.EASY));
      myWords.addWord(new Word("Besmirch", Diff.MEDIUM));
      myWords.addWord(new Word("Pulchritudinous", Diff.HARD));
      myWords.addWord(new Word("Dog", Diff.EASY));

      System.out.println(myWords);
      myWords.sortByPrio();
      System.out.println(myWords);
   }
}

Is anything inherently wrong with my code above, regarding my implementation of the Comparator? If so, what should I improve? Also, I haven't redefined equals, which I usually do when I implement Comparable. Should I redefine it now as well?