English and Scottish.
Elsie was derived late in the 19th century from Elspeth, via its mainly Scottish pet form, Elspie. In the 20th century it began to be used as an independent name and overtook Elspeth in popularity.Â It may also be a pet name for Elsa and for Elizabeth/Elisabeth.
Not to be confused with Ailsa with which it has no connection.
Elsie is a rare pet name for Alison, itself a diminutive of Alice. A correspondent [JW] has noted an example where Elsie and Alice have been used interchangeably so we have classified Elsie as a pet name for Alice as well.