Ask a Teacher: Dead as a Doornail

idiomatic - adj. using, containing, or denoting expressions that are natural to a native speaker

idiom - n. an expression that cannot be understood from the meanings of its separate words

nail - n. a long, thin piece of metal that is sharp at one end and flat at the other end and that is used usually to attach things to wood

feather - n. any one of the light growths that make up the outer covering of the body of a bird

clam - n. a type of shellfish that lives in sand or mud and has a light-colored shell with two parts