According to Mark,
Lochlannach, -aich, -aich nm Norwegian, Norseman, Scandinavian, Viking □ the meaning ‘Norwegian’ is not common now. To avoid confusion Nirribheach (q.v.) is used instead
Lochlannach a Norwegian, Norse, Scandinavian
Lochlannais nf Norse (lang.)
I am sure that in practice it would have meant the place you get to if you cross the North Sea. Gaelic geography over there may have been a bit hazy.
A didnae hink o hat. Aye, it's obvious the noo. Wikipedia informs us, in the origin section of Lachlan (Name)
In the ninth century, the terms Laithlinn / Laithlind (etc.), appear in historical sources as terms denoting the origin of Vikings active in Ireland. The exact meaning behind these terms is uncertain. What is clear, however, is that the terms Lochlann / Lochlainn (etc.) came to replace these earlier terms; and that, by the eleventh century, Lochlann / Lochlainn certainly referred to Norway in historical sources. Whether the terms Lochlann / Lochlainn were originally related to Laithlinn / Laithlind, or merely conflated with them, is unknown. In mediaeval Irish literature, the term Lochlann refers to a vague faraway place: sometimes the Otherworld, and sometimes Scandinavia.
and later it mentions a number of descendants including Laughlin.
Wiktionary just says Lochlann means 'land of the lochs' (i.e. fjords), without citing sources. If laithlind is the older term then presumably this got misunderstood as 'land of the lochs'. Alternatively laithlind is the mis-hearing of lochlann
- Soisgeul Mharcais Mark's Gospel (1st century AD) (note that sgeul 'story' and spel(l) are the same word
- Faclair Mharcais Mark's Dictionary (2003). Just as authoritative in its field - but obviously a different field. silmeth recommends dictionaries here. I am going to add my comments there to keep all the comments together.
It means roughly the same, right enough, but it's not quite the same construction, and the nuance in meaning is the same as in English - Tha Nirribhidh cho fuar = Norway is so cold - Norway is the subject of the verb; Tha i cho fuar ann an Nirribhidh = It is so cold in Norway - it (the weather) is the subject of the verb.