Venus' sister is referred to in two crossword solutions: SERENA (6 letters) and ATHENA (6 letters). Serena is the name of Venus' younger sister, a professional tennis player who has won 23 Grand Slam singles titles. ATHENA is the Greek goddess of wisdom, courage, inspiration, civilization, law and justice, mathematics, strength, war strategy, the arts, crafts, and skill. She is also the patron goddess of Athens.