severe, unrelenting; cruel
Latin in- + clementem 'mild'
1550s, from Middle French inclémence and directly from Latin inclementia "rigor, harshness, roughness," from inclemens (see inclement).
1660s, from French inclément and directly from Latin inclementem (nominative inclemens) "harsh, unmerciful," from in- "not, opposite of, without" (see in- (1)) + clementem "mild, placid." "Limitation to weather is curious" [Weekley].