1553, "mildness or gentleness shown in exercise of authority," from L.
clementia "calmness, gentleness," from
clementem (nom.
clemens) "calm, mild," related to
-clinare "to lean" (see
lean (v.)). Meaning "mildness of weather or climate" is 1667;
clement (adj.) is older in both senses, 1483 and 1622 respectively, but now is used only in negation and only of the weather.