Definition: Word choice. Diction is the foundation of voice and contributes to all of its elements. Diction creates the color and texture of the written work; they both reflect and determine the level of formality; they shape the reader’s perceptions.
Effective voice is shaped by words that are clear, concrete, and exact. Good writers eschew words like pretty, nice, and bad. Instead they employ words that invoke a specific effect. A coat isn’t old; it is tattered. The United States Army does not want revenge; it is thirsting for revenge. A door does not shut; it thuds.
Understanding diction will help you to analyze better and to write better. Learn the meaning of diction to identify and analyze in a text and learn to use more precise diction in your own writing. (from Voice Lessons by Nancy Dean)