The name Billi is a short form of the female given name Wilhelmina, which is derived from the German masculine name Wilhelm. Wilhelm comes from the Germanic elements "wil" meaning "will" or "desire", and "helm" meaning "helmet" or "protection". Therefore, the name Billi means "strong-willed protection" or "resolute protection".
The name Wilhelmina was first used as a female name in Germany during the Middle Ages. It became more popular throughout Europe during the 19th century, particularly among royal families and nobility. For example, Queen Wilhelmina of the Netherlands was born in 1880 and reigned from 1890 to 1948.
The name Billi has been used as an independent given name since at least the mid-20th century. It is considered a unisex name, although it is more commonly associated with females. In recent years, the name Billi has gained popularity in English-speaking countries such as the United States and Australia.
Some notable people named Billi include American actress Billi Gordon, who was active during the 1970s and 1980s, and Australian cricketer Belinda "Billi" Clark, who played for the national team from 2004 to 2008.
The name Billi has seen a significant rise and fall in popularity over the century, with peaks in the mid-60s and early 70s, and low points in recent years.