a. | 1. | (Chem.) Pertaining to, derived from, or designating, the highest oxygen acid (HIO ) of iodine. |
| 1. | Of or pertaining to a period or periods, or to division by periods. |
| 2. | Performed in a period, or regular revolution; proceeding in a series of successive circuits; as, the periodical motion of the planets round the sun. |
| 3. | Happening, by revolution, at a stated time; returning regularly, after a certain period of time; acting, happening, or appearing, at fixed intervals; recurring; as, periodical epidemics. |
| 4. | (Rhet.) Of or pertaining to a period; constituting a complete sentence. |