Meaning

noun a mountain lake (especially one formed by glaciers)

originFrom Middle English terne, tarne (“lake; pond, pool”), from Old Norse tjǫrn (“a small lake without tributaries”), from Proto-Germanic *ternō (“water hole”), perhaps related to *turnaz (“bitter, embittered”), ultimately from Proto-Indo-European *der- (“to separate, split; to crack, shatter”). The word is cognate with Danish tjern, Faroese tjørn (“pond”), Icelandic tjörn (“pond”), Norwegian Bokmål…

Etymology from Wiktionary, CC BY-SA 3.0