Here's why:
* Noun: A character trait is a specific quality or feature of a person's character.
* Phrase: "Character trait" is a group of words that act as a single unit, in this case, functioning as a noun.
You could use "character trait" as a subject, object, or other noun-related grammatical function in a sentence.
For example:
* Subject: Honesty is a valuable character trait.
* Object: I admire her courage as a character trait.