"Double whammy" is an English idiom referring to a situation when one malady occurs in close succession to an existing one. It can be used in the case of a person or group of people having two problems to solve at the same time. In other situations, "double whammy" can be used when it seems like one bad thing happens to someone right after another unfortunate thing has occurred. The origins of the phrase come from the fact that the word "whammy" is often used to describe a hex or a curse.
Idioms are used occasionally by people when they want to use colorful language and colloquial terms to describe a common occurrence in daily life. These idioms usually take on different meanings from their original intents or even from the literal definitions of the words included. Popular usage in the culture gives them their new meanings, and many of these idioms have are used to describe situations involving bad luck. One of these idioms is "double whammy," a phrase that dates back to the first part of the 20th century.
This particular idiomatic expression gets its meaning from the colloquial definition of the slang word "whammy," which can be found in descriptions from American sportswriters in the 1930s and 1940s. When someone has the "whammy" put on them, it means that they have run into some sudden bad luck. As a result, luck that is twice as bad must mean that someone has received a "double whammy."
People often use this phrase when a pair of bad things happens to a person at the same time. Since the phrase is sometimes used for comical effect, the bad things that call it to be used often aren't overly serious. If the bad things that occur are serious and the phrase is being used, it means that the speaker is engaging in a bit of dark humor. For example, someone might say, "First my house burned down and then my wife left me; that's what I'd call a double whammy."
The phrase has expanded from that original definition that had to do with bad luck to now include any situation when problems seem to pile up suddenly. As an example, a student might say, "I've got that big final exam coming up and now I've got a paper due as well, so the professors have really hit me with a double whammy." In this case, luck isn't really involved, but two problems that must be overcome have surfaced at about the same time.