What does Drill mean?
A left hand 2×1 weave, twill fabric.
Heddels explains Drill
Made of cotton, drill is a durable fabric with a strong diagonal twill weave. The material is most often used for jackets, safari clothes, and uniforms; however, it is also sometimes used for sails, tents, and canopies because of its durability. Drill is a versatile cloth known for its strength, light weight, and breathability.
Visual of drill: