Scottish and English variant of Elisabeth/Elizabeth [q.v.], from an ancient Hebrew name meaning "oath of God".
Although references tend to record the name Elspet under Elspeth, if at all, the 1841 Census of Aberdeenshire records the spelling Elspet [q.v.] many hundreds of times more frequently than Elspeth.
While Elizabeth and Elspeth are frequently interchangeable for a single individual, one correspondent records several families in Moray, Scotland having children named Elizabeth and Elspeth living at the same time, and several other such families have been found in Aberdeenshire. It is therefore suggested that care be taken when examining old records: the occurrence of two names which can be interchangeable [i.e. synonymous] does not necessarily indicate that there is only one person!
A correspondent [GJ] has recorded many occurrences of the spelling Elspith, especially around Perth in Scotland in the late 16th century and clearly equivalent to Elizabeth.