The term 'fail to notice' can be expressed in three different ways: OVERLOOK (8 letters), MISS (4 letters), and unsee (5 letters). OVERLOOK means to fail to notice something due to carelessness or inattention, while MISS implies that something was not seen or noticed because it was too quick or subtle. Unsee is a more recent term which means to forget or ignore something, often intentionally. All three terms refer to the same concept of failing to notice something, either through negligence, speed, or intention.