The term "Clement" comes from Old French "clement" and from Latin "clementem". In both languages, it appeared as an adjective. From Latin, clement acquired its meaning of mild, placid and gentle; and from Old French, clement acquired its meaning of "mild in temper", referring to the weather.
Nowadays, the term has two broadly accepted definitions. According to the Webster Dictionary, clement is an adjective that means 1) someone inclined to be merciful and 2) mild (the weather).