- One that goes his own way
- One time
- One way or another
- One who creates
- One who deserves to be pitied
- One who enjoys
- One who feeds
- One who holds
- One who intimates
- One who is not done his duties
- One who kisses
- One who knows past -present and future
- One who makes
- One who ploughs
- One who sleeps at sunrise
- One who toil ceaselessly to support his family
- One yield
- One's pound of flesh
- One-eighth
- One-eyed
- One-stop shop
- One-tenth
- One-twelfth
- Oneness
- Onerously
- Ones evil deeds
- Ones own
- Ones own affair
- Ones soul for
- Onion
- Only
- Only just
- Ontogenesis
- Ontologist
- Oops
- Oozy
- Opacity
- Opaquely
- Open face
- Open field
- Open glass
- Open gutter
- Open heart
- Open ones eyes
- Open the mouth
- Open-eyed
- Open-mindedness
- Opened as a flower
- Opener
- Opening sale
- Operant
- Operations
- Operoseness
- Opiate
- Opined
- Opinionative
- Opiophagism
- Opportunely
- Opposed
- Opposing
- Opposite shore
- Oppositeness
- Opposition
- Oppressing others
- Oppressively
- Optant
- Opthalmologist
- Opthalmology
- Optic
- Optic angle
- Optic axis
- Optic nerve
- Optical centre
- Optical fiber
- Optical instrument
- Optimalise
- Or otherwise
- Oracy
- Oral
- Oral cavity
- Oral presentation
- Orangery
- Orator
- Oratorical
- Orbicularity
- Orbit rotation
- Orchestra
- Orchestral
- Orchestration
- Ordained
- Order
- Order about
- Ordinance
- Ordinary green colouring
- Ordnance
- Orectic
- Organic analysis
- Organic disease
- Organic farming
- Optophone