'open'-'over'
- open tubular column
- open-ended hollow cathode
- open-tube chromatography
- opening out
- operational pH scale
- operational pH standards
- operational pH-cell
- optical conductance
- optical density
- optical emission spectrometry
- optical fibres
- optical filters
- optical pumping
- optical quantities
- optical systems
- optical-signal modulation
- optically thin plasma