- ostomy bag
- ostracism in organization
- ostracod
- ostracod analysis
- ostracoderms
- Ostrava
- ostrich fern genus
- Ostriker-Peebles criterion
- Ostriker-Vishniac effect
- Ostrogothic Kingdom
- Ostrogradski, Mikhail Vasilyevich
- Ostrogradskiǐ
- Ostrogradskiǐ equation
- Ostrogradskiǐ formula
- Ostrogradskiǐ-Gauss formula
- Ostrogradskiǐ-Liouville formula
- Ostrogradskiǐ method
- Ostrogradsky
- Ostrogradsky Gauss formula
- Ostrogradsky-Gauss formula
- Ostrovskiǐ
- Ostrowski
- Ostrowski-Hadamard gap theorem
- Ostrowski inequality
- Ostrowski theorem