The term 'strength of spirit' can be defined by three crossword solutions: VALOR (5 letters), METTLE (6 letters), and MORALE (6 letters). VALOR is a quality of bravery and fearlessness, while METTLE is a measure of courage and fortitude. MORALE is the mental and emotional state of an individual or group, and is often used to describe the collective attitude of a team or organization. All three words are related to the concept of strength of spirit, as they refer to the courage and determination of individuals or groups in the face of adversity.