List of Collective Nouns: o

1. obeisance
   1. an obeisance of servants
2. observance
   1. an observance of hermits
3. obstinacy
   1. an obstinacy of buffalos
4. obstruction
   1. an obstruction of dons
5. optimism
   1. an optimism of youths
6. orchestra
   1. an orchestra of musicians
7. ostentation
   1. an ostentation of peacocks