Better knock on wood! It’s illegal to jaywalk. It must be Murphy’s Law. Everything’s OK. Sleep tight.

Stumped? Don’t be; they’re just a bunch of idioms.

The Oxford English Dictionary defines an idiom as “a form of expression, grammatical construction, phrase, etc., peculiar to a language; a peculiarity of phraseology approved by the usage of a language, and often having a significance other than its grammatical or logical one.”

Put simply, it’s an expression with an understandable meaning that wouldn’t normally make sense.

Margaret Shaw, associate professor in Kent State’s English department, said she thinks idioms usually begin with a meaning.

“I think they get started by being sort of a literal description of the way something is,” she said. “Over time, they’ve taken on figurative meanings.

“So, after a while, it doesn’t really mean what it originally meant, but can be applied to many situations,” she added.

“Sleep tight” is an idiom often heard before bed, not in the literal sense of wrapping oneself tightly in blankets, but possibly a different literal interpretation.

This form of “tight” is defined as the adverb “tightly,” meaning “soundly,” and is mainly used in the rhyming bedtime phrase, according to the dictionary. So, this implies “tight” was just another way to say “sleep soundly.”

Another theory of the phrase origin stems from an older style of bed frame where it was necessary to stretch ropes in a criss-cross pattern to create a comfortable sleeping surface, but evidence for this theory is lacking, according to Michael Quinion’s World Wide Words Web site.

Shaw said theories on word origins could come about by attempting to discover how literal meanings transform into figurative ones.

“It’s just a matter of logical figuring,” she said. She added inaccurate ideas could result from having the original saying wrong or simply not knowing.

The idea “if something can go wrong, it will” is a sentiment of Murphy’s Law, but who is Murphy and why does he have a law? In the autobiography Into Orbit by former astronaut and pilot John Glenn, Murphy is said to be a fictional mechanic from a series of educational U.S. Navy cartoons. The character was “a careless, all-thumbs mechanic who was prone to make such mistakes as installing a propeller backwards,” and isn’t the only explanation for the law’s origin.

Another probability for the idiom’s creation is Capt. Edward A. Murphy, an engineer studying deceleration for an Air Force project, according to the dictionary and an article from the Desert Wings, an Air Force newspaper. When a device was incorrectly wired, he was said to state what would become known as Murphy’s Law.

Bad luck, such as that associated with Murphy’s Law, was meant to be warded off by “knocking on wood.” The origin of this idiom is thought to come from mythology’s association between trees and good spirits or wood’s connection to the Christian cross, according to World Wide Words Web site. It was believed to be good luck to knock on trees, letting the wood spirits know someone was there. Iron was also considered lucky and used in the same way as wood.

This American version of “knock on wood” dates back to the early 20th century, but there was a British version called “touch wood” as early as the 17th century, according to The Phrase Finder Web site.

Another expression with an origin related to trees is “I’m stumped.” This probably refers to obstacles caused by tree stumps left when clearing land, according to the dictionary. The Middle English verb “stumpen,” meaning “to stumble, as if over a tree stump” evolved into the modern usage, stated Evan Morris, “The Word Detective” columnist.

The term “jaywalk” is a combination of two words, one with a more obvious meaning than the other. Pertaining to the expression, “jay” is “a stupid or silly person; a simpleton,” as defined by the dictionary.

People visiting cities, known for their lack of awareness, were called “jays,” in the 1800s, according to Morris. This may be because of blue jays’ reputation of being loud and unintelligent, but the term “jay” had been used since the 1500s to describe an unintelligent person, he stated. By the early 1900s, “jaywalking” was known as ignoring traffic signals and crosswalks.

OK is a fairly short expression with a large history. Allen Walker Read of Columbia University is credited for discovering the origin of OK, which is known to have appeared in Boston newspapers in 1839. The newspapers used a style of humor where phrases were shortened to initials, jokingly misspelled at times and explained in parentheses. In this manner, “all correct” was reduced to the initials OK.

The term OK became even more popularized by President Martin Van Buren’s 1840 re-election campaign, according to Read. Buren was nicknamed “Old Kinderhook” because of his birthplace in Kinderhook, N.Y., and the abbreviation became a campaign slogan.

The people who speak these idioms and others like them help determine which ones will continue or die out.

Shaw said phrase use depends on the phrase itself.

“I think in part, it’s how colorful they are,” she said. “They start out being a really apt description of something and then after while, because they were colorful or lively, you use them over and over again until they actually become pretty boring and dull.”

But the origins of some idioms can be anything but boring.

“It’s surprising sometimes what the original meanings are,” Shaw said. “It’s surprising to me, and I work with them all the time.”

Contact features correspondent Kelly Byer at [email protected].