I'm over the moon! Don't look a gift horse in the mouth. Turnabout is fair play.
What do all of these sentences have in common? They're examples of idioms. An idiom is a phrase that can’t be understood just by looking at the individual meanings of the words. Idioms are an example of figurative language, and while they add a lot of color to conversation or writing, they can often be difficult to understand the first time you hear them.
In fact, idioms are one of the hardest things for non-native speakers to pick up. In English alone, there are estimated to be more than 20,000 different idioms. Some idioms used to have a clear meaning, but maybe the original literal meaning has dropped away, and the intent remains.
Is that clear as mud? (That's an idiom.) Let's try to shine a light through the fog (another idiom) with some common examples.
Have Cold Feet
To “have cold feet” doesn’t mean that your feet are physically cold, but it implies that someone is nervous about a commitment or having second thoughts. Usually it’s used to talk about someone who is hesitant about getting married. Pull on a warm pair of socks and get down the aisle.
Hold Someone’s Feet to the Fire
This phrase means to put strong pressure on someone to take an action or take responsibility for something. Generally the phrase is seen as positive, as you are being strong and demanding accountability. Missing from the modern idiom's usage is the original intent of painful interrogation techniques.
Down in the Mouth
Not all idioms are about feet. This one can probably be figured out via context clues, but a new English speaker might not get it on their first try. To be down in the mouth means you're unhappy or sad. The corners of your mouth are likely turned down in a frown.
On the Fence
“On the fence” refers to being stuck between two different choices or ideas. Your mind isn’t made up, and you’re still able to be swayed one way or the other. This is a good example of an idiom where the literal meaning is similar to, but not the exact same as, the idiomatic significance.
Take a Rain Check
You might have used this one without understanding that it used to be a very literal description. If a ball game was called off on account of rain, the spectators would be given a "rain check," which would be a ticket valid for the make-up game. Today this idiom is used as an excuse for when you really don't want to do something right then and there.
Raining Cats and Dogs
This one definitely trips up non-native speakers. “Raining cats and dogs” means that it is raining very hard. Actual cats and dogs are not coming out of the sky, so grab an umbrella and you'll be fine.
Run Around Like a Chicken With Its Head Cut Off
Animals tend to provide good fodder for idioms. If you don't live on a farm, it's not likely that you've seen a headless chicken. But you can probably imagine the frenzy of such a creature. That's exactly what it's like if you're so flustered that you run around like a chicken with its head cut off.
Fortune Favors the Bold
This idiom does make sense from the definitions of the individual words, but the complete meaning of the package is a little more poetic. Think of summoning up your courage and attempting to achieve your goals. Good luck and fortune just might fall your way.