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).
子どもは熱心に平仮名をかいていた。
The child was practicing hiragana with zeal.
かれが毎朝駅前でスキップの練習をしている熱心なすがたに心打たれました。
My heart was struck by how he practiced skipping enthusiastically every morning in front of the station.
トーフグの新入社員はみんな、仕事にやる気を見せることに熱心で、寝てもいい時間でさえも、仕事をしていた。
Tofugu’s new employees were all keen to show their enthusiasm and worked even when they could have been sleeping.