In the sentence, the word daunting means intimidating.
To answer this question, we need to determine the meaning of the word "daunting" in the given sentence. One way to find the meaning is by using context clues. In this case, the sentence states that William was afraid to begin the task because he had never written more than five pages before. From this, we can infer that the task of writing his research essay was intimidating or overwhelming to him. Therefore, the correct answer is "intimidating."