Bill
Bill meaning: Form of William. Resolute guardian.
Bill origin: English
Bill gender: Male

Billie
Billie meaning: Determination, strength. A nickname for William. Often combined with other names Billie-Jean and Billie Jo.
Billie origin: English
Billie gender: Female

Billy
Billy meaning: Form of William. Resolute guardian.
Billy origin: German
Billy gender: Male