Homonym, homophone, and homograph designate words that are identical to other words in spelling or pronunciation, or both, while differing from them in meaning and usually in origin.
Homophones are words that sound alike, whether or not they are spelled differently. The words pear “fruit,” pare “cut off,” and pair “two of a kind” are homophones that are different in spelling; bear “carry; support” and bear “animal” are homophones that are spelled alike.
Homographs are words that are spelled identically but may or may not share a pronunciation. Spruce “tree” and spruce “neat” are homographs, but so are row [roh] “line” and row [rou] “fight” as well as sewer [soo-er] “conduit for waste” and sewer [soh-er] “person who sews.”
Homonyms are, in the strictest sense, both homophones and homographs, alike in spelling and pronunciation, as the two forms bear. Homonym, however, is used more frequently than homophone, a technical term, when referring to words with the same pronunciation without regard to spelling. Homonym is also used as a synonym of homograph. Thus, it has taken on a broader scope than either of the other two terms and is often the term of choice in a nontechnical context.