The term 'strength of will' can be described by two crossword solutions: GRIT (4 letters) and BACKBONE (8 letters). GRIT is defined as courage and resolve; strength of character. It is often used to describe someone who is determined and has the courage to face difficult challenges. BACKBONE is defined as strength of character, courage, and determination. It is often used to describe someone who is strong-willed and stands up for what they believe in. Both terms are used to describe someone who has the strength of will to overcome any obstacle.