1. Last in an indefinitely numerous series
   - umpteenth, umteenth

See also: ordinal

• family Nyctaginaceae
• family Nymphaeaceae
• family Nymphalidae
• family Nyssaceae
• family Ochnaceae
• family Ochotonidae
• family Octopodidae
• family Odobenidae
• family Odontaspididae
• family Oedogoniaceae
• family Oestridae
• family Ogcocephalidae
• family Oleaceae
• family Oleandraceae
• family Onagraceae
• family Oniscidae
• family Ophidiidae
• family Ophiodontidae
• family Ophioglossaceae
• family Opisthocomidae
• family Opisthognathidae
• family Orchestiidae
• family Orchidaceae
• family Orectolobidae
• family Oriolidae