The difference between Blessing and Boon

When used as nouns, blessing means some kind of divine or supernatural aid, or reward, whereas boon means a prayer.

Boon is also adjective with the meaning: good.

check bellow for the other definitions of Blessing and Boon

Blessing as a noun:

Some kind of divine or supernatural aid, or reward.
Blessing as a noun:

A pronouncement invoking divine aid.
Blessing as a noun:

Good fortune.
Blessing as a noun (paganism):

A modern pagan ceremony.
Blessing as a noun:

The act of declaring or bestowing favor; approval.

Examples:

"We will not proceed without the executive director's blessing.'"
Blessing as a noun:

Something someone is glad of.

Examples:

"After two weeks of sun, last night's rainfall was a blessing."
Blessing as a noun:

A prayer before a meal; grace.
Blessing as a noun:

A group of unicorns.

Boon as a noun (obsolete):

A prayer; petition.
Boon as a noun (archaic):

That which is asked or granted as a benefit or favor; a gift or benefaction.
Boon as a noun:

A good thing; a blessing or benefit; a thing to be thankful for.

Examples:

"Finding the dry cave was a boon to the weary travellers."

"Anaesthetics are a great boon to modern surgery."
Boon as a noun (UK, _, dialectal):

An unpaid service due by a tenant to his lord.

Boon as an adjective (obsolete):

good; prosperous; as, "boon voyage"
Boon as an adjective:

kind; bountiful; benign
Boon as an adjective:

(Fossil word used only in idiom pairing it with subsequent "companion") gay; merry; jovial; convivial

Boon as a noun:

The woody portion of flax, separated from the fiber as refuse matter by retting, braking, and scutching.