Enthusiasm
Passion, Zeal
noun, な adjective
When your heart is feverish and hot about something, it is obviously something you have a lot of enthusiasm about. Think about the things you've enthusiasm for. Then, imagine your heart beating and getting all hot from thinking about it. Why else would people get so upset when talking about religion and politics. It's their feverish heart! Their enthusiasm!
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. Be careful of the ねっ portion (normally is ねつ).
みんな、とても熱心に先生の話を聞いていましたよ。
Everyone listened to the teacher very attentively.
このアイドルグループには熱心なファンがたくさんいる。
This idol group has many devoted fans.
サオリさんの母親はとても教育熱心です。
Saori's mother is very passionate about education.