The name Enborg is constructed from two Swedish words: "en" and "borg". "En" means juniper and "borg" means castle, tower or stronghold.
It is "fictitious" in so far as it was a name which was assumed by different unrelated people who had patronymic names, both in Sweden and Swedish emigrants to America.
Around the turn of the last century it was quite common for people with patronymic names (Andersson, Johansson, Svensson, Larsson and so on) to take new names which were more unique. These names were often constructed by two word elements, one often with some biological meaning, such as a word for a species of tree, a lake, a mountain and so on.