These words are based on a common element, the Greek term homo, meaning "same." A homonym is a word like another in sound and spelling but different in meaning: "the bow of a boat" and "to make a bow"; "the bark of a dog" and "the bark on a tree." A homograph is a word of the same written form as another but of different origin and meaning and possibly of pronunciation: sole ("only," or part of a shoe); wound ("injury," and the past tense of wind). A homophone is a word pronounced the same as, but differing in meaning from, another, whether spelled the same way or not: key and quay, tear and tier, heir and air.
Dictionary of problem words and expressions. Harry Shaw. 1975.