"To the nines" is an English idiom meaning "to perfection" or "to the highest degree" or to dress "buoyantly and high class". In modern English usage, the phrase most commonly appears as "dressed to the nines" or "dressed up to the nines".
Origin
The phrase is said to be Scots in origin. The earliest written example of the phrase is from the 1719 Epistle to Ramsay by the Scottish poet William Hamilton:
Robert Burns' "Poem on Pastoral Poetry", published posthumously in 1800, also uses the phrase:
References
To the nines Wikipedia(Text) CC BY-SA