This summer I learned the slang “what’s the craic” from this interview:
Craic is pronounced like crack in English, and the whole phrase means something like “what’s new” or “what’s up”. Delightful! I regret only having learned it this recently.
Craic would be an odd English spelling. Turns out it was borrowed from Irish pretty recently, within the last 40 years or so. But before that, craic was borrowed into Irish from the English crack, as a Gaelicized spelling of it, not too long before craic was re-borrowed into English.
Crack in that sense of “news” or “chat” came from Northern England and Scotland, as a softening of an earlier usage of crack that meant “loud boasting”. And that crack traces back to the Middle English word crak, meaning the same. Crak in turn comes from Old English cracian, meaning to make a sudden sharp noise.
What about “crack shot”, you’re now asking. From Northern England and Scotland, usage of crack to mean “loud boasting” worked its way south. As it did, its meaning shifted more towards describing what was being boasted about. So if your “crack” was being a good marksman, then eventually I could call you a “crack shot”.
But remember this ultimately derives from cracian, a sudden sharp noise; a word you would use to describe a gunshot. So modern English in essence re-purposed a term from Old English, that was borrowed via Middle English into Scots and Northern English.