1. Memorable for being a special occasion
   "on red-letter nights a large gathering greeted the celebrity"

See also: unforgettable

• Onopordon acanthium
• Onopordum
• Onopordum acanthium
• Onosmodium
• onrush
• Onsager
• onset
• onshore
• onside
• onslaught
• onstage
• Ontarian
• Ontario
• ontic
• onto
• ontogenesis
• ontogenetic
• ontogeny
• ontological
• ontologically
• ontologist
• ontology
• onus
• onward
• onward motion