- apostatic behaviour
- a posteriori
- a posteriori bound
- a posteriori distribution
- a posteriori error estimate
- a posteriori estimate
- a posteriori mean
- a posteriori probability
- a posteriori risk
- A Post Horse
- Apostichopus japonicus aestivation
- apostilb
- Apostle
- apostle of the Slavs Constantine
- Apostol
- apostolic delegate
- apostolic internuncio
- apostolic nuncio
- apostolic prefect
- apostolic prefecture
- Apostolic See
- apostolic vicariate
- A Postscript to the Postscript of Calligraphy and Painting
- apothem
- apothem of a regular polygon