1. Loud enough to shake the very earth 
2. Sufficiently significant to affect the whole world
   "earthshaking proposals"
   - world-shaking, world-shattering, earth-shattering

See also: important, loud, significant

• cliff
• cliff diving
• cliff dweller
• cliff dwelling
• cliff penstemon
• cliff rose
• cliff swallow
• cliff-brake
• cliff-hanging
• cliffhanger
• Clifford Odets
• Clifford trust
• Cliftonia
• Cliftonia monophylla
• climacteric
• climactic
• climate
• climate change
• climatic
• climatic zone
• climatical
• climatically
• climatological
• climatologist
• climatology