Answer:
The best answer to the question: What reference source would you use to find the meaning of "etiquette", would be: dictionary.
Explanation:
When talking about sources of information to comprehend a word, we have two of them: dictionary and thesaraus. While a thesaurus does not define a word directly, but rather leads to comprehension through giving clusters of related words (synonyms and antonyms), a dictionary does directly define the meaning of the word, without necessarily mentioning the synonyms and antonyms for that word. In this case, the word etiquette is not of English origin but French and therefore, to comprehend it, find its meaning, we need to use a dictionary to understand exactly what it means.