The difference between Mournful and Sorry

When used as adjectives, mournful means filled with grief or sadness, whereas sorry means regretful for an action.

Sorry is also interjection with the meaning: expresses regret, remorse, or sorrow.

Sorry is also noun with the meaning: the act of saying sorry.

check bellow for the other definitions of Mournful and Sorry

Mournful as an adjective:

Filled with grief or sadness; being in a state in which one mourns.
Mournful as an adjective:

Fit to inspire mourning; tragic.

Sorry as an adjective (of a person):

Regretful for an action; grieved or saddened, especially by the loss of something or someone.

Examples:

"I am sorry I stepped on your toes. It was an accident."

"I am sorry to hear of your uncle's death."
Sorry as an adjective:

Poor, sad or regrettable.

Examples:

"The storm left his garden in a sorry state."
Sorry as an adjective:

Pathetic and inferior to the point of causing others disgust.

Examples:

"Bob is a sorry excuse for a football player."