The term INTENSE EFFORT can be described by two crossword solutions: STRAIN (6 letters) and FORCE (5 letters). STRAIN is defined as an intense effort or exertion, while FORCE is defined as the application of strength or power to achieve a desired result. Both terms refer to the use of physical or mental energy to accomplish a goal. Intense effort is often required to achieve success in any endeavor, whether it be physical, mental, or emotional.