The term 'not well-defined' can be described by two crossword solutions: 'HAZY' (4 letters) and 'DIM' (3 letters). Both words refer to something that is not clear or distinct, and can be used to describe a lack of definition. HAZY implies a lack of clarity due to a fog or mist, while DIM implies a lack of brightness or vividness. Together, these two words can be used to describe something that is not well-defined.