Kuwaiti is the word for a person from Kuwait, or for anything that belongs to that country — a Kuwaiti passport, Kuwaiti oil, Kuwaiti food. The place itself is Kuwait, a small, very rich oil state in the Middle East, at the top of the Persian Gulf, with Saudi Arabia to the south and Iraq to the north. In 1990 Iraq invaded and took it over; that started the Gulf War. In 1991 a US-led force pushed Iraq out, and people still reach for that war when they say the word. The capital is Kuwait City, and most people live in or around it. Though actually, a large share of the people living there are workers from other countries, not Kuwaiti citizens — so “Kuwaiti” is tighter than “someone who lives in Kuwait”. As a noun you can say “a Kuwaiti”; as an adjective it just marks origin. It is a plain nationality word, not slang and not fancy.