NCI Dictionary of Cancer Terms

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The NCI Dictionary of Cancer Terms features 7,916 terms related to cancer and medicine.

Browse the dictionary by selecting a letter of the alphabet or by entering a cancer-related word or phrase in the search box.

pupil
(PYOO-pul)
The round opening in the center of the iris (the colored tissue that makes the "eye color" at the front of the eye). The pupil changes size to let light into the eye. It gets smaller in bright light and larger as the amount of light decreases.