Welcome to January, the two-faced month. On the one hand, it’s the start of the new year, a time to make resolutions and look forward to fresh beginnings. On the other hand, it’s a time to look backward, when you shred a lot of last year’s documents and tax forms arrive to remind you how well (or poorly) you did last year.

January is named for Janus, the Roman god of beginnings and ends. Janus guarded doorways, which represent the beginning of one space and the end of another, and was also said to guard the gates of heaven. He is usually pictured as a two-faced figure, one looking to the left, the other to the right.

Janus has lent his name to more than months. That two-timing friend who deceives you is “Janus-faced,” not a positive image. But a “Janus friend” can also be looking ahead or behind you, to protect you. (There’s even an investment company that markets itself that way.)

And then there are “Janus words.” (Bet you were wondering when we would get around to language.) Like the other “Janus” uses, they are two-faced.

“Janus words,”—also known as “contranyms” and “contradictanyms,” which are more fun to say but less lyrical—have two meanings that are opposite each other. This column has talked about one of those, sanctioned, which, depending on context, can either mean to approve (a “league-sanctioned game”) or to punish, as in what happened to Rep. Charles B. Rangel. Another Janus word that can cause confusion depending on your location is “table”: In British usage, it means to bring to a vote; in American usage, it means to delay taking a vote.

If you were told to “cleave” a rope, you might not know whether you’re supposed to cut it apart or bring it together. Similarly, if you were asked to “clip” something, you don’t know if you’re supposed to attach it or trim it. And if you were asked to help a friend “trim” her Christmas tree, you might have been surprised when she handed you a set of clippers instead of ornaments.

A “custom” like a tree-trimming party is something usual, while you hope the “custom” suit you wear to the party is not. You can “dust” the table to remove the powdered sugar that drifted when you “dusted” the gingerbread. A movie that is “screened” is shown to everyone, unless the movie rating is “R,” to “screen” sensitive young eyes. If you visibly “secreted” sweat while watching that horror movie but “secreted” it from your kids, you’ve honored Janus, too. If your kids see the movie anyway because of an “oversight” on your part, it may be that you lacked “oversight.” Slang loves Janus words, too. “Cool,” “sick,” and “bad” all are positive in slang, but negative in traditional usage. And someone who says “temper, temper” if you get angry is really telling you to soften your outburst.

For most Janus words, context will let you “dig” it. But if you don’t pick it up “fast,” you may be stuck “fast.”

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Merrill Perlman managed copy desks across the newsroom at The New York Times, where she worked for 25 years. Follow her on Twitter at @meperl.