mononucleosis
Concise Oxford English Dictionary © 2008 Oxford University Press:
mononucleosis /ˌmɒnə(ʊ)njuːklɪˈəʊsɪs/
▶noun Medicine an abnormally high proportion of monocytes in the blood, especially associated with glandular fever.
'mononucleosis' also found in these Oxford entries:

