open slating - overheating
- order of assembly
- order of crystallization
- order of erection
- order of execution of works
- order of march
- order specification
- ordered state
- orderly progress of the work
- orderly urban development
- ordinal relation
- ordinance
- ordinand
- ordinary
- ordinary brick lintel
- ordinary cinder aggregate
- ordinary construction
- ordinary dense concrete
- ordinary leveling
- ordinary painting
- ordinary Portland cement
- ordinary prismatic key
- ordinary structural concrete
- ordinate
- ordinate of a point
- ordination
- Ordnance bench mark
- ordnance datum
- Ordnance Survey map
- ordnance-datum
- ordure
- ore
- ore washer
- Oregon pine
- organic
- organic aggregates
- organic architecture
- organic binder
- organic bonded grinding wheel
- organic chemistry
- organic compound