Passionate Enthusiasm, Passionate, Vehement
Noun and な adjective
ねつれつ
彼女はどうやらお前の熱烈なファンみたいだな。
She seems to be a passionate fan of yours.
This fever is violent. This is the feeling you get when you have crazy passionate enthusiasm, aka you are impassioned.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.