Metropolitan Opera, theˌMetropolitan ˈOpera, the (also the Met informal) 
a US opera company based at the Lincoln Center for the Performing Arts in New York City
a US opera company based at the Lincoln Center for the Performing Arts in New York City- on-board
- once
- Once in Royal David's City
- once-over
- oncologist
- oncology
- oncoming
- Ondaatje, Michael
- one
- O'Neal, Shaquille
- one another
- one-armed bandit
- one-dimensional
- One Flew Over the Cuckoo's Nest
- one-horse
- One Hundred and One Dalmatians
- O'Neill, Eugene
- one-liner
- one-man
- one-man band
- One Nation Party
- oneness
- one-night stand
- one-off
- one-on-one