Dressed up to the nines

This means to be dressed very smartly or extravagantly. But why 'to the nines?'

Many years ago, when Britain had Imperial currency - also called 'old money' which was in Pounds, shillings and pence, the expensive seats in a cinema or theatre were high up and cost ninepence. It was something special to go there and you needed to be dressed very smartly - up to the nines!

And, what more important theatrical occassion than the big speech from Hamlet!