Drill is a burly cotton fabric similar to denim that’s woven in a pronounced diagonal twill. The most common use of drill is in the construction of khakis. The word khaki refers to the color of the garment, and drill is the most common material dyed khaki. This is because British soldiers stationed in India during the 1840s wore drill uniforms and found that dying them a khaki color made good camouflage in the dusty surroundings.