Khakis are trousers made of khaki cloth — a strong cotton in a dull yellow-brown, the colour of dust. In American English especially, “khakis” means that kind of casual trousers; people wear them to school, to the office on a freer day, or at the weekend. The word is informal-to-neutral. You almost always hear the plural when you mean the pants: “I’m wearing khakis.” British English is more likely to say “khaki trousers.” Though actually, speakers stretch it a lot. Many people say khakis for any similar tan or beige cotton trousers, even when the cloth is not true old military khaki. Soldiers used that cloth so they would not stand out against dry ground; the school-and-office trousers came later. The colour word is khaki; the trousers are khakis.