- open items list (US), deficiency report, lack report
- overhaul a machine (engine)
- open, (Stelle) vacant
- oil separator (crankcase)
- oil scraper ring (piston)
- oil reservoir, oil container
- oil flange (crankshaft)
- oil filter, lube-oil filter
- oil baffle, oil deflector
- oil-pressure indicator (manometer)
- oil feed-back (distribution)
- oil pan, oil sump
- oil duct, oil feed
- optical fiber (fiber GB)
- on time, punctual; (Zahlung) prompt payment
- oscillate, vibrate; (wirtschaftlich) fluctuate
- oscillation damper, vibration damper
- opt for, decide
- optional equipment, optional features, special features
- out-of-flat, uneven
- open, unfinished, outstanding (order)
- overstress; (Gewicht) overload; (Heizung) overload; overload
- order, sequence
- objective (strategic), goal, aim, target (operative)
- objective variable, auxiliary controlled variable
- omnidirectional microphone, non-directional microphone
- operating panel, operator control panel; control panel
- oval-head screw, lentil-head screw
- oval head, lentil head
- oil press
- one-lane
- one-man band
- online bank
- online service
- op. cit.
- order check
- ordinary negligence
- organ bank
- out-of-office reply
- outside capital
- overcaution
- overeagerness
- overexcitement
- oxer
- oxygenic
- Old Catholic
- of a different faith
- opening column
