Idiom: Dressed to the nines
Meaning: Extremely well-dressed, dressed flamboyantly
Example: "That New Year's Eve party was very fancy. Everyone was dressed to the nines."
Origin: There are several theories surrounding the origins of this phrase. One of the more popular explanations is that a bolt of fabric is made up of nine yards, and that the whole bolt is used to make a fine suit. This would also appear to explain the origins of the phrase "the whole nine yards," but unfortunately it explains neither. A bolt of fabric is comprised of from between 40 and 100 yards, depending on the material.
While no definitive origin for "to the nines" has been found, there is general agreement among etymologists that it relates to the historical use of the number nine as a superlative. There are nine muses in classical mythology, cats are said to have nine lives, and the number nine is significant in Norse, Greek, Egyptian, and Native American mythology.
Nine is the highest single-digit number, which is most likely why it was used to describe the ultimate, the supreme, and the maximum. Which is why any etymologist who found the true origins of the phrase "dressed to the nines" would surely be described as being "on cloud nine."