Related Clues:

• Has enough marbles
• Right-minded
• Soothe
• At peace
• Playing will a full deck, so to speak
• Capable of thinking clearly
• Tranquillity
• Realistic
• Serenity
• Less than 1 m.p.h., as winds
• Sailboater's woe
• Not out of one's mind
• Sensible, and alternate title of this puzzle
• Serene
• Clear-headed