spinnaker (SPIN-uh-ker) - n., on a yacht, a large triangular headsail used when running before the wind.

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The one belling out in front -- and because it's fastened by the three corners, there's no way to use it except with the wind coming from behind. This is very much a yachting terms: although there are mentions of the term in larger ship's logs, for any of various jib staysays, it was widely used only when the sail started to be added to yachts in the 1860s. Its exact origin is unknown, tho' there's plenty of stories about possible origins.
---L.

Thanks, WikiMedia!
The one belling out in front -- and because it's fastened by the three corners, there's no way to use it except with the wind coming from behind. This is very much a yachting terms: although there are mentions of the term in larger ship's logs, for any of various jib staysays, it was widely used only when the sail started to be added to yachts in the 1860s. Its exact origin is unknown, tho' there's plenty of stories about possible origins.
---L.