battlefield or battlegroundnoun

• ophicleide
• ophidian
• ophite
• ophthalm-
• ophthalmia
• ophthalmic
• ophthalmic optician
• ophthalmo-
• ophthalmologist
• ophthalmology
• ophthalmoscope
• -opia
• opiate
• opine
• opinion
• opinionated
• opinion poll
• opium
• opium den
• opium poppy
• opossum
• opp.
• opponent
• opportune
• opportunism