The difference between Mediocre and Ordinary

When used as nouns, mediocre means a person of minor significance, accomplishment or acclaim, whereas ordinary means a devotional manual.

When used as adjectives, mediocre means having no peculiar or outstanding features, whereas ordinary means having regular jurisdiction.

check bellow for the other definitions of Mediocre and Ordinary

Mediocre as an adjective:

Having no peculiar or outstanding features; not extraordinary, special, exceptional, or great; of medium quality.

Examples:

"I'm pretty good at tennis but only mediocre at racquetball."

Mediocre as a noun:

A person of minor significance, accomplishment or acclaim; a common and undistinguished person.
Mediocre as a noun (historical):

A member of a socioeconomic class between the upper ranks of society and the agricultural workers.

Ordinary as an adjective (legal, of a judge):

Having regular jurisdiction; now only used in certain phrases.
Ordinary as an adjective:

Being part of the natural order of things; normal, customary, routine.

Examples:

"On an ordinary day I wake up at nine o'clock, work for six hours, and then go to the gym."
Ordinary as an adjective:

Having no special characteristics or function; everyday, common, mundane; often deprecatory.

Examples:

"I live a very ordinary life most of the time, but every year I spend a week in Antarctica."

"He looked so ordinary, I never thought he'd be capable of murder."
Ordinary as an adjective (Australia, New Zealand, colloquial, informal):

Bad or undesirable.

Ordinary as a noun (obsolete):

A devotional manual.
Ordinary as a noun (Christianity):

A rule, or book of rules, prescribing the order of service, especially of Mass.
Ordinary as a noun:

A person having immediate jurisdiction in a given case of ecclesiastical law, such as the bishop within a diocese.
Ordinary as a noun (obsolete):

A set portion of food, later as available for a fixed price at an inn or other eating establishment.
Ordinary as a noun (archaic, _, or, _, historical):

A place where such meals are served; a public tavern, inn.
Ordinary as a noun (heraldry):

One of the standard geometric designs placed across the center of a coat of arms, such as a pale or fess.
Ordinary as a noun:

An ordinary thing or person; the mass; the common run.
Ordinary as a noun (historical):

A penny-farthing bicycle.