1. No longer in existence; lost or especially having died out leaving no living representatives
   - extinct 
2. No longer existing or inaccessible through loss or destruction
   "its nonextant original was written on vellum"

See also: dead, nonexistent

• order Myxosporidia
• order Naiadales
• order Neuroptera
• order Nidulariales
• order Notostraca
• order Nudibranchia
• order Octopoda
• order Odonata
• order oedogoniales
• order of business
• order of magnitude
• Order of Our Lady of Mount Carmel
• order of payment
• order of Saint Benedict
• order of the day
• Order of the Purple Heart
• order Oleales
• order Ophioglossales
• order Opiliones
• order Opuntiales
• order Orchidales
• order Ornithischia
• order Orthoptera
• order Ostariophysi
• Order Osteoglossiformes