O字母開頭的單詞或詞組(第17頁)：

• once a week
• on show
• outwards
• overcritical
• on top of
• optic nerve
• offing
• off the rack
• open-circuit voltage
• orthodontology
• opulent
• overpressure
• owlet
• over here
• onym
• operation mode
• ocean
• octal numberal
• oneirodynia
• optimum
• Orizaba jalap
• oximeter
• overmatch
• otoscope
• ossa
• open a case
• on request
• observer
• offer subject to sample approval
• once too often
• out of use
• one's complement
• open bid
• open circuit
• ordinal number
• orthopneic
• on fire
• official document
• of purpose
• Oedipus complex
• obturator sign
• occult