Fishing nets with mesh size designed so fish can push their heads through but get caught by their gills when they try to back out.
From 'gill' (fish respiratory organ, from Old Norse 'gjölnir') + 'net' (from Old English 'nett'). The compound term emerged in the 19th century as fishing technology became more specialized and documented.
Gillnets are so effective that they've been banned in many countries because they indiscriminately catch whales, dolphins, and sea turtles—a tragic reminder that the 'best' fishing method isn't always the most ethical one.
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