The name Billie is a girl's name of English origin meaning "resolute protection". Billie and is often added to lists like Nicknames for Girls and discussed in our forums with posts like "Release the 20 C.O.B.R.A.S. -- the anti-elimination game! (Girls)".
From the experts:
Billie is a tomboy nickname name, part of the growing trend for using boyish nicknames for girls.
To track its path from blue to pink, Billie was 100% male in 1880, was 55% female just a decade later, in the girls' Top 100 by 1928, and is now overwhelmingly female.
Billie is a possible retro choice for fans of jazz great Billie Holiday, born Eleanora. Other conceivable namesakes are The Wizard of Oz's Glinda--Billie Burke (born Mary William), silent screen star Billie Dove (born Bertha), actresses Billie Whitelaw and Billie Piper (born Lianne) and tennis legend Billie Jean King (born Billie). Another cultural reference is the Michael Jackson hit song 'Billie Jean.'
Billie was picked for their daughters by Carrie Fisher, My Name is Earl actor Ethan Suplee, and Rebecca Gayheart and Eric Dane.