Gain altitude is a term used to describe the action of an aircraft or other object increasing its altitude, or height, in the air. The four crossword solutions for this term are SOAR, CLIMB, ASCEND, and RISE. SOAR is an action that involves gliding through the air with little effort, while CLIMB is an action that requires more effort and energy to ASCEND. ASCEND is a more gradual increase in altitude, while RISE is a sudden increase in altitude.