The word "恒久" is formed by combining the character "恒", meaning constant or perpetual, which incorporates the heart radical (忄) with "亘" to suggest extended continuity, and the character "久", meaning long-lasting or enduring, derived from a pictogram representing duration. Together, they create a compound where "恒" emphasizes steadfastness and "久" emphasizes longevity, resulting in the meaning of everlasting or permanent.