| IO | converting totally or partly into ions |
|---|---|
| IO | high-energy radiation capable of producing ionization in substances through which it passes |
| IO | the outer region of the Earth's atmosphere |
| IO | a sky wave that is reflected by the ionosphere |
| IO | Russian Soviet leader |
| IO | the 9th letter of the Greek alphabet |
| IO | a tiny or scarcely detectable amount |
| IO | an informal debt instrument |
| IO | a dialect of the Chiwere language spoken by the Iowa people |
| IO | a state in midwestern United States |
| IO | a member of the Siouan people formerly living in Iowa and Minnesota and Missouri |
| IO | wild crab apple of western United States with fragrant pink flowers |