Possible Clues:

• Reasonable grounds detailed
• Having common sense or reason
• Sound
• Make allowance with a half-century with reason
• Sane and sensible
• Perhaps Sun's leader replaced? That's sensible
• Levelheaded
• It stands to reason to make an allowance of a half a century
• Sensible with the animal; a lion, trained
• Thinking — not a liar (anag)