back·pres·sure 
(băkprĕsh′ər)
(băkprĕsh′ər)n.
Residual pressure opposing the free flow of a gas or liquid, as in a pipe or an exhaust system.
- proconsulate
- proconsulship
- Procopius
- procrastinate
- procrastination
- procrastinator
- procreant
- procreate
- procreation
- procreative
- procreator
- Procrustean
- Procrustean bed
- procryptic
- proctitis
- proctodaeum
- proctodeum
- proctologic
- proctological
- proctologically
- proctologist
- proctology
- proctor
- proctorial
- proctorship