plural of birthday party

Unclothed.

plural of birthday attack

(rare) An unclothed person.

(historical) A book, in diary form, in which one's friends enter their birthdates in their own handwriting.

plural of birthday book

plural of heavenly birthday

A birthday of a person after his or her death.

(probability theory) The counterintuitive observation that a random group of people needs to have only 23 members before there is a 50% chance of two of them having the same birthday.

plural of birthday suiter