Related Clues:

• Littlest bit
• Greek letter after theta
• Homeric character
• Bit for 38-Across
• "We have split the ___"
• Molecule building block
• With 4-Across, mushroom cloud producer
• Very small bit
• Electrons' place
• Small sorority letter?
• Building block of nature
• Jot, e.g.
• Extremely small amount
• Bond part
• Tiny trace