- ornamental brick
- ornamental brickwork
- ornamental enamel
- ornamental glass
- ornamental painting
- ornamental tile
- ornamental work
- ornamentation
- ornamented architecture
- orogenesis cycle
- orphan
- orphan asylum
- orthistyle
- oscillatory impulse
- ordinary beam
- ordinary coordinates
- ordinary gravel
- ordinary pitch
- ordovocian period
- ore mucking
- ore ship
- organic
- organic glass
- organizer
- organogenous limestone
- oriel
- orientate blasting
- orientation system
- original colors
- original edit
- ornamental castings
- ornamental composition
- ornamental gable
- ornamental panel
- ornamental parapet
- ornamentalism
- orogeny
- orographic map
- orphanage
- orthogonal
- orthographic view
- orthotropic body
- orthotropic deck
- orthotropic plate
- orthotropic shell
- orthotropic structures
- ottrelite schist
- out of
- out-port
- outcrop line
- outdoor lighting
- outdoor paint
- outer
- outer cofferdam
- outer court
- outer shoulder
- outer slope
- outermost fiber
- outfall channel
- outfall well
- outflow dish
- outlet
- outlet ditch
- outlet gate
- outlet pipe
- outlet sluice
- outlet temperature
- outlet work
- outlier
- outline
- outline drawing
- outline map
- outline welding
- outlook
- outmost fiber
- outpouring
- output
- output alphabet
- output circuit
- output control
- output device
- output information
- output message
- output rate
- outreach
- outrigger
- outrigger jack
- outrigger scaffold
- outside architrave
- outside column
- outside glazing
- outside lining
- outside shutter
- outside stairs
- outsize
- oval
- over bank
- over thrust
- over-reinforced
- overall dimensions