Step 1: Understanding the Concept:
Parts of speech categorize words based on their grammatical function within a sentence.
A noun is a word used to identify a person, place, thing, or abstract quality.
Step 2: Detailed Explanation:
In the given sentence, the word "honesty" refers to an abstract quality or state.
It functions as the subject of the sentence's action (being the thing that impressed people).
Since "honesty" refers to a concept rather than a physical object, it is classified specifically as an Abstract Noun.
An adjective would be "honest", a verb would be "honored", and an adverb would be "honestly".
Step 3: Final Answer:
The underlined word "honesty" is a Noun. Therefore, option (C) is correct.