Webster’s defines idiom as follows:

Main Entry: id·i·om

Pronunciation: \ˈi-dē-əm\

Function: noun

Etymology: Middle French & Late Latin; Middle French idiome, from Late Latin idioma individual peculiarity of language, from Greek idiōmat-, idiōma, from idiousthai to appropriate, from idios

Date: 1588

1 a : the language peculiar to a people or to a district, community, or class : dialect b : the syntactical, grammatical, or structural form peculiar to a language
2 : an expression in the usage of a language that is peculiar to itself either grammatically (as no, it wasn't me) or in having a meaning that cannot be derived from the conjoined meanings of its elements (as Monday week for “the Monday a week after next Monday”)
3 : a style or form of artistic expression that is characteristic of an individual, a period or movement, or a medium or instrument <the modern jazz idiom>; broadly : manner, style <a new culinary idiom>

As I noted in an earlier post on these funny little guys, idioms are a major stumbling block when learning a new language because a person can know the definitions of all the words in the phrase and still have absolutely no idea what the phrase means.

Here are a few more idioms along with their meanings and origins.

Dressed to the nines – Back in the days before Gentleman’s Wearhouse and other clothing chain-stores, a tailor would use more fabric when making a high quality suit. The best suits are made from nine yards of fabric. This may seem like a lot, but a proper suit does indeed take nine yards of fabric. This is because a good suit has all the fabric cut in the same direction with the warp, or long strands of thread, parallel with the vertical line of the suit. This causes a great amount of waste in suit making, but if you want to go "dressed to the nines", you must pay for such waste. And you could pay for the waste, you had deep pockets.

Dressed to a tea - A short way of saying "dressed for a tea" or "dressed to go to a tea". In the Victorian era, high tea was a formal affair. All proper people dressed in appropriate attire. For somebody of my generation, being dressed to a tea means a good suit and tie and wingtip shoes. For my children’s generation it means your best Nikes, bluejeans with no holes (or strategically placed tatters), and a tee-shirt with no offensive words on it.

Reading the riot act - "Reading the riot act" used to be a literal event. Bobbies in Britain used to read a prescribed proclamation, known as the Riot Act, before they could break up or arrest a crowd.

The Riot Act is used in a fashion similar to the Miranda Rights in the US. The Bobbies would approach the crowd, read the Riot Act aloud, and then disperse or arrest them.

So, if you were read the riot act, you were in very deep do-do.