The term 'not as SLACK' can be summarized by the crossword solution 'tauter, ' which is a six-letter word. Tauter is an adjective that means 'tightly stretched or pulled; not SLACK.' It is often used to describe rope, fabric, or other materials that are stretched or pulled tightly. It can also be used to describe a person's behavior, meaning that they are more disciplined and organized than someone who is 'SLACK.'