Lynne Murphy is an American linguist who has been living in the UK for 21 years. For 10 of them she has been writing the blog Separated by a Common Language, detailing the many ways, both subtle and obvious, American and British English part ways. No one is more of an expert on the UK/North America differences, so you can imagine her shock when she realized that all this time, the people around her had a completely different understanding of the word frown. For her, the locus of the frown was the mouth. For the Brits around her, it was not the mouth, but the brow that made the frown.

She discovered this fact through an old blog post by Michael Wagner, a linguistics professor at McGill University, where he tells the story of how he found out that frown meant something different to him (he is from Germany and has European English) than to his Canadian friend. They were looking at a piece of abstract art at a museum when his friend asked, "Do you think this is a frown or a moustache?" Wagner was confused because,

Whatever 'this' was, it was clearly below the eyes, and also, the facial expression was sad—so how could it be a frown? My understanding of frown was what I later found in Webster's online dictionary:

1 : an expression of displeasure
2 : a wrinkling of the brow in displeasure or concentration

When I expressed my puzzlement, I learned that frown, in fact, also means the opposite of smile: a downward facing mouth expressing sadness, and that this is in fact the most common/salient meaning of the word, at least to some.

What is a frown? A look of displeasure, made with the eyebrows? Or a sad face, made with downturned mouth? Informal surveys performed by Wagner at the time and then six years later by Murphy both revealed the same result, which can be summed up as "Wait! OMG! THAT’S what you think it means? I had no idea!" And "Oooohhh, so that’s why Americans say ‘turn that frown upside down'!"

So what’s a frown to you? The opposite of a smile or a furrowed forehead of concern?

Check out Wagner’s original post, and read the very interesting ensuing discussion at Separated by a Common Language, which suggests there may be age and regional effects influencing your decision.