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1. Relating or belonging to or serving as a monument
   "the use of the arch in monumental architecture"; "monumental sculptures"
    
2. Of outstanding significance
   "Einstein's monumental contributions to physics"
    
3. Imposing in size or bulk or solidity
   "a monumental scale"
   - massive, monolithic

See also: big, important, large, monument, significant

Encyclopedia: Monumental