[almostarockstar]

Leeway: The "lee" is the area downwind of a vessel. A lee-shore is a shoreline that the wind blows on to, as opposed to a windward shore that the wind blows off. To give leeway is to allow enough room for a vessel to be blown off course by the wind and avoid danger.

Rig (noun): The mast and supporting stays on a boat. (oil rigs, "big rig" come from this I think).

Rig (verb): To put the sails up and tie on the sheets and other lines that control sails. ("Let's rig this up." == "Let's set this up.")

Posh (my favourite, though I doubt it's actually true): Port Out Starboard Home. When travelling from England to India around the tip of Africa, it was favourable to have a cabin on the port side on the way to India and starboard on the way back as it would be in the shade most of the time and a little cooler in the sun, with a view of the land.

See also: Change tack / try a different tack, right the ship, stay the course, (to be) swamped, "At a rate of knots" (very fast), keep an even keel, keel over.

[ttepasse]

I too doubt the posh etymology: If you’re sailing around the cape by definition you will have crossed the equator twice, meaning your calculation of the sun positions will change. Acronyms pronounces as words seem more a modern 20th century thing.

Wiktionary talks about posh coming from the Romani language, meaning half, in monetary terms, as in half a crown. Seems believable to me, a lot of modern terms come from traveller’s languages and argots and such. See also tory and whig.

[blackshaw]

The "posh" one is commonly repeated, but there's no evidence it's true: https://www.etymonline.com/word/posh#etymonline_v_18515

[unwind]

That is pretty cool!

Swedish (also picking a lot from German, of course) has the same word ("lä", and no I'm not going to try to describe the pronunciation) but our usage is wider in scope. In Swedish lä is simply "out of the wind", and not restricted to use onboard a vessel. Cool, didn't know that about English.