Merciful, a.
Etymology: [Mercy + -ful.]
1. Full of mercy; having or exercising mercy; disposed to pity and spare offenders; unwilling to punish. The Lord, the Lord God, merciful and gracious. Ex. xxxiv. 6. Be merciful, great duke, to men of mold. Shak.
2. Unwilling to give pain; compassionate. A merciful man will be merciful to his beast. Old Proverb.
Syn. -- Compassionate; tender; humane; gracious; kind; mild; clement; benignant. -- Mer"ci*ful*ly, adv. -- Mer"ci*ful*ness, n.
Shades of meaning
Fernald has no entry of its own for merciful; he lists it under humane, propitious.
Where he writes about it:
The humane man will not needlessly inflict pain upon the meanest thing that lives; a merciful man is disposed to withhold or mitigate the suffering even of the guilty. — from humane