A cubit — a unit of measure based on the length of the forearm (approximately 18 inches). Jesus used it to illustrate the futility of worry: no one can add a single cubit to their life by worrying.
Jesus asked: 'Can any one of you by worrying add a single hour to your life?' (Matthew 6:27). The literal Greek says 'a single cubit to your stature/lifespan.' Worry is not just spiritually harmful — it is utterly ineffective. It cannot change reality by even the smallest measurement. Only trust in God produces genuine change.