In modern usage, by speakers of Scottish English, it means "smelly". I'm not 100% sure, but I'm confident that "reek" in this context was borrowed from Scots and the meaning has just drifted over time.
Scottish Gaelic (Gàidhlig) and Irish Gaelic (Gaeilge, often just called "Irish") are both direct descendants of Middle Irish, which ultimately comes from a Celtic root. Gaidhlig gradually replaced Pictish, now extinct, about a thousand years ago.
In modern usage, by speakers of Scottish English, it means "smelly". I'm not 100% sure, but I'm confident that "reek" in this context was borrowed from Scots and the meaning has just drifted over time.
Its etymology is interesting, and it consistently means "smoke" or "smoking": https://www.etymonline.com/search?q=Reek
Scottish Gaelic (Gàidhlig) and Irish Gaelic (Gaeilge, often just called "Irish") are both direct descendants of Middle Irish, which ultimately comes from a Celtic root. Gaidhlig gradually replaced Pictish, now extinct, about a thousand years ago.