Related Clues:

• With 51-Across, singer's latest
• Certain fingerprint
• Present but unseen
• Unheard of
• NYC part
• Previously unheard of
• 'What's --?'
• Under the surface
• ''Brave ___ World''
• Brand-spanking ___
• Out-of-the-box
• Never done before
• "So, what else is ___?"
• Opposite of full
• Present but inactive