What's the name of a list with only one element

Question

What is the 'formal' name of a list that has only one element?

Answer 1

Java Collections calls this a singleton list, although I don't think this is a formal name.

public static List singletonList(T o) Returns an immutable list containing only the specified object. The returned list is serializable.

I much prefer "single element list".

Edit: It appears that singleton is a valid mathematical term for a single element set.

Answer 2

I would call it a unitList (to avoid confusion with the Singleton pattern) in mathematics a set containing only a single element is also known as a unit set