mononucleosis
noun /ˌmɒnəʊˌnjuːkliˈəʊsɪs/
/ˌmɑːnəʊˌnuːkliˈəʊsɪs/
(also informal mono)
(both North American English) (British English glandular fever)
[uncountable]- a disease that causes the lymph glands to swell (= become large, round and painful) and makes the person feel very weak for a long time