The word "乾坤" is formed by combining the character 乾, meaning heaven or the male principle, which is ideographically constructed from elements suggesting celestial movement, with the character 坤, meaning earth or the female principle, which incorporates the radical 土 for soil. Together, they create a compound term representing the universe or the duality of heaven and earth, derived directly from their foundational roles as hexagrams in the Yijing.