Definition of ommatidium in English:

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Pronunciation: /ˌɒməˈtɪdɪəm/

noun (plural ommatidia /ˌɒməˈtɪdɪə/)

Each of the optical units that make up the compound eye of an insect.
Example sentences
  • In contrast, myriapods and chelicerates mostly lack compound eyes and the ommatidia of the few groups that have compound eyes are very different from insect/crustacean ommatidia.
  • In all these animals, the larval eye continues to exist as part of the adult eye, although the number of ommatidia in the adult compound eye far exceeds the larval quantity.
  • The retina of the compound eye is organized into approximately 3000 functional units or ommatidia, each containing eight photoreceptor cells.


Late 19th century: modern Latin, from Greek ommatidion, diminutive of omma, ommat- 'eye'.

For editors and proofreaders

Line breaks: om¦ma|tid¦ium

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