Sydnei is of American origin, derived from the English surname Sydney which means "wide meadow". This name gained popularity during the mid-20th century and has since been used as both a feminine and gender-neutral given name. It consists of three syllables: Sy-dne-i. The spelling varies slightly, with Sydni being another common form. The name Sydnei is not associated with any specific saints or historical figures, nor does it have any particular religious significance. As a unisex name, Sydnei has been used for individuals regardless of their gender identity. It has appeared on the Social Security Administration's baby names list in the United States since 1978 but remains relatively uncommon, ranking outside the top 1000 most popular names.
The name Sydnei experienced a boom in popularity from the mid-1990s to around 2005, with the highest number of births recorded being 37 in 2005. However, since then, its usage has significantly declined, with only 6 births recorded in 2018 and 5 in 2019. Overall, there have been a total of 635 babies named Sydnei from 1988 to 2020.