We know that English is full of word pairs that seem like they should be opposites but actually mean the same thing, such as “caretaker” and “caregiver.” The most common construction of these “false antonyms” comes from Latin-based prefixes, which are often used in English to create real synonyms. “De-,” for example, is used to undo or reverse a verb’s action, as in "activate" vs. "deactivate." But the appearance of a prefix — such as “de-,” “un-,” or “in-” — on an otherwise matching word pair doesn’t automatically create an antonym. Let’s look at some examples of the most common “false” antonyms.
Words With the Prefix "De-"
Devoid: (Adj.) Entirely lacking or free from.
Void: (Adj.) Completely empty.
"Devoid" originally meant "cast out" in Old English, but came to mean "without," as in, "The city street was devoid of pedestrians." "Void," which seems like it should mean the opposite without the “de-” prefix, can also be used as an adjective meaning "completely empty," as in, "Thanks to his lies, the mayor’s promises were void of meaning." It came into Middle English from Old French as a word meaning "unoccupied." Thanks to both words’ evolutions, they are now synonymous. The trick here is in the parts of speech. The prefix “de-” reverses actions from verbs. “Void” here is an adjective, but it can also be a noun, meaning “a completely empty space.”
Of course, there are always exceptions in English. Here are some examples of “de-” being added to verbs, where the definitions remain essentially the same, maybe with a slightly different usage.
Bone: (Verb) To remove the bones from meat or fish.
Debone: (Verb) To remove the bones from meat or fish, especially before cooking
Press: (Verb) To cause something to move by applying physical pressure or force.
Depress: (Verb) To push or pull something down into a lower position.
Bar: (Verb) To prevent or prohibit someone from doing something or going somewhere.
Debar: (Verb) To officially exclude or prohibit someone from doing something.
Words With the Prefix "In-"
The prefix "in-" often suggests that two words are antonyms, such as "activity" vs. "inactivity" and "complete" vs. "incomplete." The prefix "in-" usually means "not, opposite of, or without." A secondary (and less common) meaning of "in-" is "into, in, on, or upon." This explains why some adjectives, such as "flammable" and "inflammable," can mean the same thing.
Flammable: (Adjective) Easily set on fire.
Inflammable: (Adjective) Easily set on fire.
"Flammable" and "inflammable" both describe something that can easily be set on fire. "Inflammable" is older, from the 17th century, while "flammable" was first used in the early 19th century. According to the New Oxford American Dictionary, both are correct, but "flammable" is preferred to avoid confusion.
More Examples Using "In-":
Habitable: (Adjective) Suitable or good enough to live in.
Inhabitable: (Adjective) Suitable to live in; habitable.
Valuable: (Adjective) Worth a great deal of money; extremely useful or important.
Invaluable (Adjective) Extremely useful; indispensable.
Genius: (Adjective) Very clever or ingenious.
Ingenious: (Adjective) Clever, original, and inventive.
Words With the Prefix "Un-"
The prefix "un-" almost always means "not" — "do" vs. "undo" and "limited" vs. "unlimited" — but not in every case. "Un-" also has a lesser-known meaning: "completely."
Ravel vs. Unravel
Ravel: (Verb) To untangle or unravel something; fray.
Unravel: (Verb) To undo (especially of twisted, knitted, or woven threads).
To "unravel" something and to "ravel out" something are the same thing, as in, "She unraveled her yarn" or "She raveled out her yarn." "Ravel" also means "to confuse or complicate" — "He raveled their travel plans by being late to the flight." This relates to the oldest use of "ravel" as a noun to mean a "tangle, cluster, or knot," as in "a ravel of daisies." "Ravel" is a centuries-old word that likely came from the Dutch term ravelen, meaning "to fray out, tangle."
More Examples Using "Un-":
Loosen: (Verb) To make less tight or firm.
Unloosen: (Verb) To undo or let free; unloose.
Thaw: (Verb) To become liquid or soft as a result of warming.
Unthaw: (Verb) Thaw or cause to thaw.
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