The Scottish National Party (SNP) has a secondary leadership role titled "Depute Leader". In other Westminster-system parties this role is called "Deputy Leader". In fact, sometimes SNP people use the term "Deputy Leader".
I get the impression that the SNP party prefers the term "Depute Leader", and everyone should use the term. However, I can't find an official statement explaining the term and the reasons for its use.
What is the origin of this title "Depute Leader"? Why does the SNP use this word "depute" instead of "Deputy"? Does this word with this meaning get used in other contexts than the SNP leadership?