Blessing, n.
Etymology: [AS. bletsung. See Bless, v. t.]
1. The act of one who blesses.
2. A declaration of divine favor, or an invocation imploring divine favor on some or something; a benediction; a wish of happiness pronounces. This is the blessing, where with Moses the man of God blessed the children of Israel. Deut. xxxiii. 1.
3. A means of happiness; that which promotes prosperity and welfare; a beneficent gift. Nature's full blessings would be well dispensed. Milton.
4. (Bib.)
2 more senses
A gift. [A Hebraism] Gen. xxxiii. 11.
5. Grateful praise or worship.
Shades of meaning
Fernald has no entry of its own for blessing; he lists it under mercy.
Where he writes about it:
Grace is favor, kindness, or blessing shown to the undeserving; forgiveness, mercy, and pardon are exercised toward the ill-deserving. — from mercy