| Monikko | omicrons |
| Monikko | omicra |
(sometimes capitalized) The 15th letter of the Classical and Modern Greek alphabets (16th in Ancient and Old Greek), used in ordering lists as in naming (astronomy) the 15th star of a constellation or (epidemiology) the 15th discovered major variant of a disease.
Detail from a fifth-century BCE inscription of Draco's law on homicide, showing the use of O rather than Ω in the phrase "ΠΡΟΤΟΣ ΑΧΣΟΝ" (πρώτος ἄξων, "first axon")