If you are consumed by thoughts of the word "ephemeral," and find yourself using it whenever possible, you might have onomatomania, an obsession with a particular word.
Lots of people savor beautiful words and names — particularly poets and etymologists and, sometimes, English teachers. An extreme love of a word, though, can veer into onomatomania. If the word you're obsessed with is susurrous, which means "whispering or hissing," you might note the susurrous sound of the wind in the trees and the susurrous noise of the steaming tea kettle. Onomatomania can also mean "fear of a word" or "frustration at not being able to think of a word."