n. (informal)
25B6; noun a rowing ace : EXPERT, master, genius, virtuoso, maestro, adept, past master, doyen, champion, star; informal demon, hotshot, wizard, whizz; Brit. informal dab hand; N. Amer. informal maven, crackerjack.
amateur.
25B6; adjective an ace tennis player : EXCELLENT, first-rate, first-class, marvellous, wonderful, magnificent, outstanding, superlative, formidable, virtuoso, masterly, expert, champion, consummate, skilful, adept; informal great, terrific, tremendous, superb, fantastic, sensational, fabulous, fab, crack, hotshot, A1, mean, demon, awesome, magic, tip-top, top-notch; Brit. informal smashing, brilliant, brill.
mediocre.