The term 'MOST DIFFICULT' can be described by two crossword solutions: 'HARDEST' (7 letters) and 'TRICKIEST' (9 letters). Both words refer to something that is very difficult to do or achieve. The word 'hardest' implies that the task is physically or mentally challenging, while the word 'trickiest' suggests that the task is complex and requires a lot of skill or knowledge. Both words are used to describe tasks that are extremely difficult to complete.