What does 熱心 mean?
熱心 is a Japanese noun meaning “enthusiasm” in English. It is written as 熱心 in kanji, ねっしん in hiragana, and nesshin in romaji. This word is part of JLPT N4 vocabulary.
Example sentence
この本は彼の熱心な研究の成果である。
This book is a result of his enthusiastic research.