A homonym is a word that sounds the same as another one but is spelled differently. In my 30-year career as a newspaper editor, these are the most common homonym errors I encountered: The most common mistake I saw was substituting "it's" for "its" as a possessive pronoun. With the exception of "mine," all pronouns are made possessive by adding an "s": Hi(s), hers, its, ours, theirs, yours. There is but one use for "it's," as a contraction for "it is." There is no such thing as "its'" as a possessive. Ditto for "yours'," both of which I often see. -- Principle/principal: There is just one use for the word "principle," fundamental, as it beliefs or truths. "Principal" has three meanings: A noun denoting chief importance (like a school principal, which we call headmasters in the U.S.), an adjective with the same meaning, and the base payment of a mortgage. -- Brake/break: Although these two words have very different meanings, they are often used in each other's places. -- Complaisant/complacent: The first means affable and cheerfully obliging. The second means self-satisfied or smug. -- Compliment/complement: This is very frequently used incorrectly. "Compliment" means to praise. "Complement" means to fill out or make whole. -- Stationary/stationery: The first means to stay in a fixed spot. The second is a noun for writing paper and envelopes and other office supplies. -- Pour/pore: "Pour" means to dispense a liquid; "pore" is to carefully examine, or is a noun for a tiny opening. -- Metal/mettle: The first meaning is obvious. The second means courage or spirit. -- Discreet/discrete: Again, these two are very often confused. "Discreet" means circumspect, careful, or showing good judgment (as in "a discreet inquiry"). The second means unattached or unrelated. -- Horde/hoard: The first is a disorganized or thronging crowd. The second is an accumulation of valuables, often hidden Memorize this list, and every time you encounter one of these words when writing, slow down and think twice before using it.