| Term | Definition |
|---|---|
| Obi | Obi – Wide sash word around the waist with a kimono. |
| Ogee | Ogee – A pointed arch with a curve near the apex. |
| Oil Paint | Oil Paint – A paint in which natural oil-usually linseed-is the medium that binds the pigments. |
| Oolite | Oolite- The small round particles which make up a sedimentary rock. On mass they look just like fish eggs. |
| Open Competitive Selection | Open Competitive Selection – When clients such as government agencies advertise impending bids so that anyone interested in the project who meets qualifications may submit a bid. |
| Open Grain | Open Grain – A wood grain where the annual growth rings are pronounced and there is an obvious difference between the pore size of springwood and summerwood. Oak and ash and examples of open-grained wood. |
| Open Specification | Open Specification – A bid specification written in such a way as to allow multiple numbers of products for the item being required. |
| Opencast | Opencast – The method of mining near the surface, by cutting into it from above rather than digging underground. |
| Orders | Orders – Columns influenced by the Greeks and Romans are placed into specific orders, such as Doric, Ionic, Corinthian, Composite, and Tuscan. |
| Oriel | Oriel – A bay window supported by corbels or brackets. Normally found on the second story of a home. |
| Origami | Origami – Art of folding paper to form figures and objects. |
| Overburden | Overburden – The unusable rock and matter lying over the stone to be quarried. |
| Overflow | Overflow – A pipe in bathtubs and lavatories used to prevent flooding. The pipe is located just below the rim or top edge of these fixtures. |
| Overlay Door | Overlay Door – The door is on the outside of the frame and, when closed, the door hides the frame from the view. |