Miosis

//maɪˈoʊsɪs// noun

noun ·Rare ·Advanced level

Definitions

Noun
  1. 1
    Contraction of the pupil of the eye. abbreviation, alt-of, contraction, countable, uncountable

    "Horner's syndrome consists of typically unilateral miosis and eyelid ptosis, and absent forehead sweating."

  2. 2
    Alternative spelling of meiosis. alt-of, alternative, countable, obsolete, uncountable

    "Though some condemn rhetoric as the mother of lies, speaking more than the truth in hyperboles, less in her miosis, otherwise in her metaphors, contrary in her ironies, yet is there excellent use of all these […]"

  3. 3
    reflex contraction of the sphincter muscle of the iris in response to a bright light (or certain drugs) causing the pupil to become smaller wordnet
  4. 4
    (genetics) cell division that produces reproductive cells in sexually reproducing organisms; the nucleus divides into four nuclei each containing half the chromosome number (leading to gametes in animals and spores in plants) wordnet

Synonyms

All synonyms
light reflexlight reflexmeiosismeiosismyosispupillary reflex

Example

More examples

"Technically, drugs that cause miosis can relieve the PNS effects of those causing mydriasis since sympathetic and parasympathetic stimulation tend to negate each others' effects."

Etymology

Etymology 1

From Ancient Greek μύω (múō, “to close the eyes”) + -osis.

Etymology 2

From Ancient Greek μείωσις (meíōsis).

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Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.