- on paper
- on passage
- on position
- on presentation
- on probation
- on purpose
- on rail
- on resistance
- on risk
- on sale
- on shipboard
- on shore
- on site
- on spot
- on state
- on strike
- on structure
- on tap
- on term
- on time
- on tour
- on trial
- on-air
- on-carriage
- on-carrier
- on-costman
- on-ding
- on-drive
- on-end
- on-hold
- on-hook
- on-lending
- on-licence
- on-line
- on-off
- on-period
- on-screen
- on-stream
- onager
- onagraceae
- onagraceous
- onagri
- onanism
- onanistic
- once
- once again
- once more
- once-over
- once-through
- oncer
- onchocerciasis
- onchocercosis
- onchosphere
- oncogene
- oncogenesis
- oncogenic
- oncogenicity
- oncogennesis
- oncogenous
- oncography
- oncologic
- oncological
- oncologist
- oncology
- oncolysis
- oncometer
- oncoming
- oncoming product
- oncosis
- oncosphere
- oncospore
- oncotic pressure
- oncotomy
- ondograph
- ondometer
- ondoscope
- ondulet reducer
- one
- one diaphragm
- one dimension
- one p
- one page
- one phase
- one piece
- one shipment
- one shot
- one thing
- one time
- one-address
- one-aloner
- one-another
- one-celled
- one-decker
- one-dimensional
- one-directional
- one-electron
- one-eyed
- one-fluid
- one-fourth
- one-frequency