I am just assuming that there is no term for "1" because it would just be implied. If someone were telling you to check the door to make sure it was locked, they would ask, "Did you check the door?" That would be when the "1" would come in. But if he/she asked you, "Did you double check?", then that would be where the "2" (double) would come in. Pls, share your ideas or comments.