Which of the following sources should a student consult to find the definition of the word "unattainable"?

Question

Quizplus · Accepted Answer

A dictionary is the best tool to use for finding the definition of words. In this case, the student in question would search a dictionary to find the definition of the word "unattainable". 
A thesaurus is incorrect. A thesaurus is a tool that lists words in groups of synonyms. If the student in question were looking for synonyms for the word "unattainable", then this would be the best option. However, the student is only looking for the definition, making "a dictionary" the best option. Therefore, this is incorrect.
An encyclopedia is incorrect. An encyclopedia is a set of books that give information on many topics, or many aspects of one subject. Since the student in question is interested in knowing only the definition of the word "unattainable", this is incorrect. 
A translator is incorrect. A translator is a person or tool that is used to help people understand the meaning of something in different languages. Since the student in question is interested in finding only the definition of "unattainable", this is incorrect.

Which of the Following Sources Should a Student Consult to Find