British vehicle registration for Birmingham
• Military observation post
• Old Persian (language)
• old prices
• Insurance open policy
• Theatre opposite prompt side (i.e. actor's right)
• Ordo (or Ordinis) Praedictatorum (Latin: (of the) Order of Preachers; Dominicans)
• organophosphate
• osmotic pressure
• Colloquial other people (or people's; see also under OPM; OP's)
• out of print
• outpatient
• overproof (of alcohol)
• Chem. oxide precipitate