A biting fly, especially a horsefly or similar insect that bites livestock and humans; a gad-fly.
From Old Norse 'klegg' or 'kleggi,' referring to a biting insect. The word is primarily Scottish and Northern English, and it has remained relatively unchanged for over a thousand years.
The word 'cleg' is so obscure today that even most English speakers have never heard it, yet it was a common term for farmers and rural workers—it's a reminder that specialist vocabularies from pre-industrial life have almost vanished from English, taking with them precise names for things we now ignore.
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