Possible Clues:

• Corroborate in accordance with common authentication method
• Corroborate where Nabokov placed comma?
• Form the basis for
• Support from beneath, needing identification
• Reinforce from below
• Knock dinner up to try to prevent collapse
• Strengthen from below
• 22 Across from below
• Support below leg
• Maybe use too few items plucked from cushion or bolster