Dressed to the nines

Dresses to perfection/high class or the highest degree

e.g. I went on a date recently. I was not impressed because my date arrived in scruffy jeans and a t-shirt yet I had dressed to the nines!

“To the nines” was used widely in English with the above meaning. In modern usage, it is only applied to making a huge effort in getting dressed up.
Its first use is in early 1700s Scottish poetry.
Nine is the most troublesome number in etymology. There are several phrases of uncertain parentage that include the word. Examples are, cloud nine, nine days' wonder and the whole nine yards. We can add 'dressed to the nines' to that list.