lymphocytePronunciation: /ˈlɪmfə(ʊ)sʌɪt/Definition of lymphocyte noun Physiology a form of small leucocyte (white blood cell) with a single round nucleus, occurring especially in the lymphatic system. Derivatives lymphocyticPronunciation: /-ˈsɪtɪk/ adjective lymphocyte in other Oxford dictionaries Definition of lymphocyte in the US English dictionary