noun

A playing card with a single spot on it, ranked as the highest card in its suit in most card games.

the ace of diamonds

adjective

Very good.

excellent,very good,first-rate,first-class,marvellous,wonderful,magnificent,outstanding,superlative,formidable,virtuoso,masterly,expert,champion,fine,consummate,skilful,adept

transitive verb

(in tennis and similar games) serve an ace against (an opponent).