Dressed to the nines

There are a number of theories about the origin of this expression - which was first recorded in the late 18th century in poems by Robert Burns -, but none of these theories are supported by evidence.
One explanation tries to connect the number nine to the nine Muses or with the sacred number 9 in numerology (3x3), representing perfection. Another theory takes it back to the Medieval English saying "dressed to then eyen", which meant dressed stylishly from toes up to the eyes ("to then eyne"). Over time the letter n could have shifted one space to the right by the same principle that caused "a norange" to change into "an orange", changing "eyne" into "neyne" and eventually "nines".
One last suggestion is that a tailor making a high quality suit uses more fabric. 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