The surname Maclachlan is an Anglicised form of the Gaelic Mac Lachlainn which is the patronymic form of the Gaelic personal name Lochlann meaning "stranger". Lochlann was originally a term to describe Scandinavia, composed of the elements loch (meaning "lake" or "fjord") + lann (meaning "land").
Meanings and history of the name Lachlan: | Edit. Lochlainn means "Of the lake" / "from the land of lakes", a reference to Norway which was called Lochlann in Scotland. Thus, it used to refer to a Viking ancestor.
