The term 'preoccupied one' can be defined as an 'obsessor', which is an 8-letter word. An obsessor is someone who is preoccupied with a certain topic or activity, often to the point of obsession. They are usually so focused on their task that they neglect other aspects of their life. Obsessors are often seen as driven and ambitious individuals, but can also be viewed as overly obsessive and compulsive.