Related Clues:

• Tetra- doubled
• Quadri- times two
• Prefix meaning 27-Down
• Prefix with -valent
• Bi- cubed
• Eight, as a prefix
• Prefix for "eight"
• Hedron intro
• Two times tetra-
• Tetra- + tetra-
• 81-Across, as a prefix
• Prefix with "gon"
• Ten: Pref
• Ten, for openers?
• Two-thirds of dodeca-