1. The quality or state of being mercurial; changeability, unpredictability, or volatility in mood or behavior.
Usage: Plural form of mercurialness; Often used in formal or academic contexts
2. The quality of being lively, quick-witted, or intellectually active.
Usage: Less common usage; Often associated with mental agility or cleverness

Examples

• The mercurialnesses of the stock market made it difficult for investors to predict trends.
• Her mercurialnesses in temperament kept her friends guessing about her moods.
• The artist's mercurialnesses were reflected in the constantly shifting styles of his work.
• Political leaders sometimes display mercurialnesses that undermine public trust.
• The mercurialnesses of spring weather require flexible wardrobe planning.
• His intellectual mercurialnesses made him an engaging but unpredictable conversationalist.