NCI Dictionary of Cancer Terms

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The NCI Dictionary of Cancer Terms features 7,777 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.

lethargy
(LEH-thur-jee)
A condition marked by drowsiness and an unusual lack of energy and mental alertness. It can be caused by many things, including illness, injury, or drugs.