The outward appearance of a particular trait is called the?
The outward characteristic of a particular trait is commonly known as its phenotype. This can easily be remembered if you learn that the Greek root of the word phenotype come from the word phainein. The bases of the word phainein mean "to show" and "type". Phenotype literally translates to mean "to show type" which is what you are looking for.
The answer is phenotype.