back·ache 
(băkāk′)
(băkāk′)n.
An ache or pain in the back, especially the lower back.
- petrolatum
- petroleum
- petroleum coke
- petroleum ether
- petroleum jelly
- petrolic
- petrologic
- petrological
- petrologically
- petrologist
- petrology
- Petronius
- "Petronius Arbiter."
- Petropavlovsk-Kamchatski
- Petropavlovsk-Kamchatskiy
- petrosal
- petrous
- Petrozavodsk
- Petrus
- Petrópolis
- PET scan
- PET scanner
- pet-sitter
- pet-sitting
- petter