| OCCUPIER | tradesman |
| OILMAN | sold the oil for lamps |
| OLITOR | kitchen gardener (from Olitory-a kitchen garden) |
| ORDERLY | soldier who functioned as a servant for an officer |
| ORDINARY KEEPER | innkeeper |
| ORRERY MAKER | made a mechanical apparatus for showing the movements of the planets (named after the Earl of Orrery the inventor) |
| ORRICE WEAVER | designer of lace patterns to be woven with silk thread and silk |
| OSIER PEELER | removed bark from willow rods or osiers which were used in basket weaving, usually women and children (also known as withy peelers) |
| OSTIARY | monastery door keeper |
| OUT CRIER | auctioneer |
| OUTWORKER | worker who carried on their occupation at home, e.g., cotton or woollen weavers but it applies to many occupations |
| OVERLOOKER | superintendent or overseer, especially in the textile mills |
| OVERMAN | supervisor in a colliery who checked the miners work and the quality of the mined coal |
| OWLER | sheep or wool smuggler |
| OYSTER DREDGER | member of the crew on board an oyster fishing boat |
