Clemency, n.; pl. Clemencies.
Etymology: [L. clementia, fr. clemens mild, calm.]
1. Disposition to forgive and spare, as offenders; mildness of temper; gentleness; tenderness; mercy. Great clemency and tender zeal toward their subjects. Stowe. They had applied for the royal clemency. Macaulay.
2. Mildness or softness of the elements; as, the clemency of the season.
Syn. -- Mildness; tenderness; indulgence; lenity; mercy; gentleness; compassion; kindness.
Shades of meaning
Fernald has no entry of its own for clemency; he lists it under mercy.
Where he writes about it:
Clemency is a colder word than mercy, and without its religious associations, signifying mildness and moderation in the use of power where severity would have legal or military, rather than moral sanction; it often denotes a habitual mildness of disposition on the part of the powerful, and is matter rather of good nature or policy than of principle. — from mercy
Leniency or lenity denotes an easy-going avoidance of severity; these words are more general and less magisterial than clemency; we should speak of the leniency of a parent, the clemency of a conqueror. — from mercy