Vocabulary in A Man Named Dave

A Man Named Dave is a great book and has very good, challenging words, one of them being mononucleosis. In the book, it says, "After a quick examination at the base's clinic, I was rushed to the hospital and admitted for severe mononucleosis." (Pelzer 98) After looking up the definition of this word, I now know it means the presence of an abnormally large number of mononuclear leukocytes, or monocytes, in the blood. I have never heard of or seen this word before so it challenged me when I came across it.