Meaning of “mononucleosis” - Learner’s Dictionary

mononucleosis

noun [ U ] uk /ˌmɒnəʊˌnjuːkliˈəʊsɪs/ us US UK glandular fever

an infectious disease that makes your glands (= small organs in your body) swell and makes you feel tired

(Definition of “mononucleosis” from the Cambridge Learner’s Dictionary © Cambridge University Press)