The origins of "dressed to the nines" are murky. One commonly repeated explanation suggests a connection to the nine muses of ancient Greece, who inspired creativity and beauty. Being "dressed to the nines" could hint at embodying all the grace and refinement these nine muses — including Clio, Thalia and Calliope — represented.
It could also be in reference to another group of nine, the Nine Worthies, which are part of pagan and Jewish history.
One very persistent theory links the phrase to military uniforms, where "dressed to the nines" referred to soldiers in exquisitely smart uniforms ready for inspection.
In Scottish poetry, phrases like "bonny lines" and "the whole nine yards" appear, which some believe share the same principle of going all out. There's also the theory that the phrase was at one point heard incorrectly.
But despite these frequent attempts to connect the dots, none of the supposed explanations stands out as the definitive origin. The troublesome number nine has left room for debate. This phrase likely grew out of several cultural influences rather than one clear source.