ace

A playing card with a single spot, usually the highest value.

"He played the ace of spades."

An unreturnable serve in tennis or a hole-in-one in golf.

"Murray served an ace."

Of the highest quality; excellent or superb.

"That's an ace idea!"

A person who is highly skilled or proficient at something.

"She's an ace at tennis."

To achieve a perfect score or perform exceptionally well.

"She aced her exams."