The term 'clearness of mind' can be described by three words: lucency, DAY, and LUCIDITY. Lucency is a seven-letter word meaning 'the quality of being easily seen through or understood, ' while DAY is a three-letter word meaning 'a period of 24 hours.' Lastly, LUCIDITY is an eight-letter word meaning 'the quality of being clear, logical, and easy to understand.' Together, these three words describe the concept of having a clear and logical mind.