Related Clues:

• Furnish with funds
• Do some celebrity backing
• Back, as a candidate
• Spine
• Lend support to
• Speak in favor of
• Give support to
• With 15-Across, 'Same to you, buddy'
• Give one's backing
• Plug a product, e.g.
• Sign the back
• Before hoe or down
• Sign, in a way
• Returned
• Missing word in 21-, 31-, 40- and 50-Across, applied literally