| osmium tetroxide | |
| —n | |
| a yellowish poisonous water-soluble crystalline substance with a penetrating odour, used as a reagent and catalyst in organic synthesis. Formula: OsO4 | |
| a chattering or flighty, light-headed person. |
| an arrangement of five objects, as trees, in a square or rectangle, one at each corner and one in the middle. |