Lenience, Leniency, n.
The quality or state of being lenient; lenity; clemency.
Shades of meaning
Fernald has no entry of its own for leniency; he lists it under mercy, patience.
Where he writes about it:
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