The difference between Peculiar and Unusual

When used as nouns, peculiar means that which is peculiar, whereas unusual means something that is unusual.

When used as adjectives, peculiar means out of the ordinary, whereas unusual means unlike what is expected.

check bellow for the other definitions of Peculiar and Unusual

Peculiar as an adjective:

Out of the ordinary; odd; strange; unusual.

Examples:

"The sky had a peculiar appearance before the storm."

"It would be rather peculiar to see a kangaroo hopping down a city street."
Peculiar as an adjective:

Common or usual for a certain place or circumstance; specific or particular.

Examples:

"Kangaroos are peculiar to Australia."
Peculiar as an adjective (dated):

One's own; belonging solely or especially to an individual; not shared or possessed by others.
Peculiar as an adjective (dated):

Particular; individual; special; appropriate.

Peculiar as a noun:

That which is peculiar; a sole or exclusive property; a prerogative; a characteristic.
Peculiar as a noun (UK, canon law):

an ecclesiastical district, parish, chapel or church outside the jurisdiction of the bishop of the diocese in which it is situated.

Unusual as an adjective:

Unlike what is expected; differing in some way from the norm.

Examples:

"His behavior was unusual in that it was considered childish for a man of his age."
Unusual as an adjective:

Not usual.