Would assume it’s some derivative of kilo.

It is kilo, engineers when designing a bridge also use kips which stands for thousands of lbs.

Comes originally from Ancient Greek χίλιοι which means a thousand, this became "kilo" in French, others got it from French

Kathousand

Kith

The “K” for thousand comes from the Greek word “kilo”, which means a thousand… so basically, every time you see “$10K,” it’s just the universe trying to sound fancy in Greek so your money seems smarter than you.