As if reading and writing English is not difficult enough, the language includes a number of words with opposite meanings within themselves. These are often called Janus words, after Janus, the Roman god of doors and beginnings. (January, the first month of the year, is named for him.) Janus usually was represented in art as having two bearded faces that faced in opposite directions, as do doors — and as do Janus words.

Among the most commonly encountered Janus words are cleave, hew, and sanction. For example, one can be said to cleave a block of wood, meaning to split it, or to cleaveto one’s principles, meaning to cling to them. Hew is almost synonymous in both senses. When a lumberjack hews a tree, he is cutting it down, but a politician who hews to a party platform, or a party line, is adhering closely to it. (Party line, by the way, usually is associated with the Communist Party, but is a lot older:  Senator Thomas Hart Benton of Missouri used it in a political context in a memoir published in 1854.) Sanction, meanwhile, may refer either to formal approval or permission, as in “Some states now sanction gay marriage,” or to an official ban, penalty, or deterrent, as in “The Treasury Department has imposed sanctions on Japan’s biggest organized-crime syndicate, known as the yakuza” (New York Times, Feb. 24, 2012).

Other Janus words – and this is just a selection – include to scan, meaning either to look carefully (“The captain scanned the horizon with binoculars”) or to glance quickly at (“She scanned the report in a few minutes”); to peruse, with similar senses, meaning both to read or examine carefully and to look at or read casually without much attention to detail; inflammable, easy to burn, and an especially treacherous term since the in- prefix is sometimes considered to be  a negative, with the result that the highly combustible word is understood as meaning “not flammable,” and  to trip, to catch one’s foot and stumble or, conversely, to step along nimbly.

For connoisseurs of language, an especially delicious J-word is the use of oversight when referring to congressional committees that are supposed to exercise oversight, meaning watchful supervision of governmental agencies. But an oversight also is a careless omission or mistake. After revelation in 1975 of lapses by the Senate Select Committee on Intelligence in reining in the Central Intelligence Agency, Theodore Sorensen, onetime speechwriter for President John F. Kennedy, noted that “The word ‘oversight’ has two meanings, and they chose the wrong one.”

The wordplay that characterizes slang also exploits Janus effects. For example bad can stand for “very good, excellent, wonderful, sexy” in different contexts. This usage is older than you might think. The earliest example of bad in a good sense in J. E. Lighter’s monumental but sadly as-yet unfinished Historical Dictionary of American Slang comes from 1897. It didn’t become common until much later, however. In Manchild in the Promised Land, a memoir about coming of age in Harlem in the 1950s, Claude Brown recalled at one point: “The slang had changed. . . . when somebody would say something about a bad cat, they would mean he was good. Somebody would say, ‘That was some bad pot,’ meaning it was good.”

Variations on this theme include not bad, not half bad, and not so bad, which translate as “good,” “pretty good,” or, depending on intonation — “Not bad!” — as “very good.”  Thus, a New York Times reporter, when presented with a generous slice of fruitcake, figuratively licked his lips, acknowledging that “While unlikely to win the hearts and minds of those born after the so-called Greatest Generation, it was, to be sure, not bad. Not bad at all” (March 9, 2013).

Even worse than bad is wicked, which is truly evil, but also is a Janus word in some contexts,  meaning “really good, excellent, wonderful.” Wicked seems to have acquired its “good” side more recently than did bad. The oldest example of the positive sense of the word in the historically organized Oxford English Dictionary is from the jazz age: “Tell’em to play ‘Admiration’! shouted Sloane. . . . Phoebe and I are going to shake a wicked calf” (F. Scott Fitzgerald, This Side of Paradise, 1920).

Wicked may also be used as an intensifier, signifying “very, extremely,” as in a complimentary review of a book for young adults: “Even if ‘Gorgeous’ . . . never quite realizes its full potential, it is still a wicked good time” (New York Times Book Review, May 12, 2013).

Similar to Janus words are what might be called Janus sentences, which have been constructed, usually deliberately, to be so ambiguous that opposing meanings can be read into them. These are especially useful when one is asked to write a letter of recommendation and wants to be honest but not to risk being sued for slander. For example, “You’ll be lucky to get Jones to work for you” could be understood to mean that Jones will be a fine employee – or that once employed, he’ll hardly ever do any work.

“You’ll never catch Jones goofing off or playing computer games” may just mean that Jones is too smart to be caught. Then there is the book review credited to Dorothy Parker: “It is not a novel to be dismissed lightly.” She added, however: “It should be thrown aside with great force.”

Enjoy!